I've translated the php-text-statistics package to Ruby, you can view
the files below. Please note I couldn't get the Gunning Fog Score to
work 100%

Regards,
Adam

############### Code
require 'collections/sequenced_hash'

module ReadabilityIndices

  class Readability

    NumDecimalPlaces = 1

    Titles = SequencedHash.new
    Titles[:flesch_kincaid_grade_level] = 'Flesch-Kincaid Grade level'
    Titles[:flesch_kincaid_reading_ease] = 'Flesch-Kincaid Reading
Ease'
    Titles[:gunning_fog_score] = 'Gunning-Fog score'
    Titles[:coleman_liau_index] = 'Coleman-Liau Index'
    Titles[:smog_index] = 'SMOG Index'
    Titles[:automated_readability_index] = 'Automated Readability
Index'

    attr_accessor :text
    def initialize(text = '')
      self.text = clean_text(text)
    end

    def valid_index?(index)
      Titles[index] ? true : false
    end

    def flesch_kincaid_grade_level
      round(0.39 * average_words_per_sentence + 11.8 *
average_syllables_per_word - 15.59, NumDecimalPlaces)
    end

    def flesch_kincaid_reading_ease
      round(206.835 - 1.015 * average_words_per_sentence - 84.6 *
average_syllables_per_word, NumDecimalPlaces)
    end

    def gunning_fog_score
      round((average_words_per_sentence +
percentage_words_with_three_syllables(false)) * 0.4, NumDecimalPlaces)
    end

    def coleman_liau_index
      round(5.89 * letter_count / word_count - 0.3 * sentence_count /
word_count - 15.8, NumDecimalPlaces)
    end

    def smog_index
      round(1.043 * Math.sqrt((words_with_three_syllables * (30 /
sentence_count)) + 3.1291), NumDecimalPlaces)
    end

    def automated_readability_index
      round(4.71 * letter_count / word_count + 0.5 * word_count /
sentence_count - 21.43, NumDecimalPlaces)
    end

    Colon = ": "
    Separator = ", "
    def get_indices_as_string(indices = [], diagnostics = true)
      indices = (indices.empty? ? Titles.keys : indices)
      str = indices.inject([]){|arr, index| arr << "#{Titles[index]}#
{Colon} #{self.send(index)}"; arr}.join(Separator)
      return diagnostics ? "words#{Colon} #{word_count}#{Separator}
sentences#{Colon} #{sentence_count}#{Separator} characters#{Colon} #
{letter_count}#{Separator}" + str : str
    end

#    private
    def clean_text(text)
      text.gsub!(/[,:;()-]/, ' ') # Replace commans, hyphens etc
(count them as spaces)
      text.gsub!(/[\.!?]/, '.') # Unify terminators
      text = text.strip + '.' # Add final terminator, just in case
it's missing.
      text.gsub!(/[ ]*(\n|\r\n|\r)[ ]*/, ' ') # Replace new lines with
spaces
      text.gsub!(/([\.])[\.\s?]+/, ".") # Check for duplicated
terminators
      text.gsub!(/[ ]*([\.])/, "#{$1} ") # Pad sentence terminators
      text.gsub!(/[ ]+/, ' ') # Remove multiple spaces
      #$strText = preg_replace_callback('/\. [^ ]+/', create_function
('$matches', 'return strtolower($matches[0]);'), $strText); // Lower
case all words following terminators (for gunning fog score)
      return text.strip
    end

    def round(num, decimals)
      (num * 10 * decimals).round / (10 * decimals).to_f
    end

    def letter_count
      self.text.gsub(/[^A-Za-z]+/, '').length.to_i
    end

    def sentence_count
      [1, self.text.split(/\.!?/).length].max
    end

    def word_count
      get_words.length
    end

    def get_words
      @words ||= self.text.split(/\s+/)
    end

    def average_words_per_sentence
      word_count / sentence_count.to_f
    end

    def average_syllables_per_word
      total_syllables / get_words.length.to_f
    end

    def total_syllables
      get_words.inject(0){|sum, word| sum + syllable_count(word)}
    end

    def words_with_three_syllables(count_proper_nouns = true)
      get_words.inject(0) do |sum, word|
        if syllable_count(word) >= 3
          if count_proper_nouns
            sum += 1
          else
            sum += 1 if word[0..0] == word[0..0].downcase
          end
        end
        sum
      end
    end

    def percentage_words_with_three_syllables(count_proper_nouns =
true)
      words_with_three_syllables(count_proper_nouns) / word_count.to_f
* 100
    end

    ProblemWords = {
      'simile' => 3,
      'forever' => 3,
      'shoreline' => 2
    }

    MultiSyllablesThatAreOne = [
      /cial/,
      /tia/,
      /cius/,
      /cious/,
      /giu/,
      /ion/,
      /iou/,
      /sia$/,
      /[^aeiuoyt]{2,}ed$/,
      /.ely$/,
      /[cg]h?e[rsd]?$/,
      /rved?$/,
      /[aeiouy][dt]es?$/,
      /[aeiouy][^aeiouydt]e[rsd]?$/,
      /^[dr]e[aeiou][^aeiou]+$/, #Sorts out deal, deign etc
      /[aeiouy]rse$/ #Purse, hears
    ]

    UniSyllablesThatAreTwo = [
     /ia/,
     /riet/,
     /dien/,
     /iu/,
     /io/,
     /ii/,
     /[aeiouym]bl$/,
     /[aeiou]{3}/,
     /^mc/,
     /ism$/,
     /([^aeiouy])\1l$/,
     /[^l]lien/,
     /^coa[dglx]./,
     /[^gq]ua[^auieo]/,
     /dnt$/,
     /uity$/,
     /ie(r|st)$/
    ]

    PrefixesAndSuffixes = [
      /^un/,
      /^fore/,
      /ly$/,
      /less$/,
      /ful$/,
      /ers?$/,
      /ings?$/
    ]

    def syllable_count(word)
      word = word.downcase.strip
      #handle problem words first
      return ProblemWords[word] if ProblemWords[word]

      #find number and delete prefixes and suffixes
      num_syllables = PrefixesAndSuffixes.inject(0) do |sum, prefix|
        word.scan(prefix){sum += 1}
        word.gsub!(prefix, '')
        sum
      end

      #remove non-word chars
      word.gsub!(/[^a-z]/is, '')

      #count word parts:
      num_syllables += word.split(/[^aeiouy]+/).inject(0){|sum,
word_part| sum + (word_part.blank? ? 0 : 1)}

      #subtract out syllables that are really one:
      MultiSyllablesThatAreOne.each{|syl| word.scan(syl){num_syllables
-= 1}}

      #add syllables that are really two:
      UniSyllablesThatAreTwo.each{|syl| word.scan(syl){num_syllables
+= 1}}

      return [1, num_syllables].max
    end
  end
end

############### RSpec tests
  include ReadabilityIndices

  describe "readability indices" do
    before(:each) do
     @readability_blank = Readability.new
    end

    it "should count simple syllable words correctly" do
      @readability_blank.syllable_count('a').should == 1
      @readability_blank.syllable_count('was').should == 1
      @readability_blank.syllable_count('the').should == 1
      @readability_blank.syllable_count('and').should == 1
      @readability_blank.syllable_count('foobar').should == 2
      @readability_blank.syllable_count('hello').should == 2
      @readability_blank.syllable_count('world').should == 1
      @readability_blank.syllable_count('wonderful').should == 3
      @readability_blank.syllable_count('simple').should == 2
      @readability_blank.syllable_count('easy').should == 2
      @readability_blank.syllable_count('hard').should == 1
      @readability_blank.syllable_count('quick').should == 1
      @readability_blank.syllable_count('brown').should == 1
      @readability_blank.syllable_count('fox').should == 1
      @readability_blank.syllable_count('jumped').should == 1
      @readability_blank.syllable_count('over').should == 2
      @readability_blank.syllable_count('lazy').should == 2
      @readability_blank.syllable_count('dog').should == 1
      @readability_blank.syllable_count('camera').should == 3
    end

    it "should count syllables on programmed exceptions" do
      @readability_blank.syllable_count('simile').should == 3
      @readability_blank.syllable_count('shoreline').should == 2
      @readability_blank.syllable_count('forever').should == 3
    end

    it "should count complex syllable words correctly" do
      @readability_blank.syllable_count
('antidisestablishmentarianism').should == 12
      @readability_blank.syllable_count
('supercalifragilisticexpialidocious').should == 14
      @readability_blank.syllable_count
('chlorofluorocarbonation').should == 8
      @readability_blank.syllable_count('forethoughtfulness').should
== 4
      @readability_blank.syllable_count('phosphorescent').should == 4
      @readability_blank.syllable_count('theoretician').should == 5
      @readability_blank.syllable_count('promiscuity').should == 5
      @readability_blank.syllable_count('unbutlering').should == 4
      @readability_blank.syllable_count('continuity').should == 5
      @readability_blank.syllable_count('craunched').should == 1
      @readability_blank.syllable_count('squelched').should == 1
      @readability_blank.syllable_count('scrounge').should == 1
      @readability_blank.syllable_count('coughed').should == 1
      @readability_blank.syllable_count('smile').should == 1
      @readability_blank.syllable_count('monopoly').should == 4
      @readability_blank.syllable_count('doughey').should == 2
      @readability_blank.syllable_count('doughier').should == 3
      @readability_blank.syllable_count('leguminous').should == 4
      @readability_blank.syllable_count('thoroughbreds').should == 3
      @readability_blank.syllable_count('special').should == 2
      @readability_blank.syllable_count('delicious').should == 3
      @readability_blank.syllable_count('spatial').should == 2
      @readability_blank.syllable_count('pacifism').should == 4
      @readability_blank.syllable_count('coagulant').should == 4
      @readability_blank.syllable_count('shouldn\'t').should == 2
      @readability_blank.syllable_count('mcdonald').should == 3
      @readability_blank.syllable_count('audience').should == 3
      @readability_blank.syllable_count('finance').should == 2
      @readability_blank.syllable_count('prevalence').should == 3
      @readability_blank.syllable_count('impropriety').should == 5
      @readability_blank.syllable_count('alien').should == 3
      @readability_blank.syllable_count('dreadnought').should == 2
      @readability_blank.syllable_count('verandah').should == 3
      @readability_blank.syllable_count('similar').should == 3
      @readability_blank.syllable_count('similarly').should == 4
      @readability_blank.syllable_count('central').should == 2
      @readability_blank.syllable_count('cyst').should == 1
      @readability_blank.syllable_count('term').should == 1
      @readability_blank.syllable_count('order').should == 2
      @readability_blank.syllable_count('fur').should == 1
      @readability_blank.syllable_count('sugar').should == 2
      @readability_blank.syllable_count('paper').should == 2
      @readability_blank.syllable_count('make').should == 1
      @readability_blank.syllable_count('gem').should == 1
      @readability_blank.syllable_count('program').should == 2
      @readability_blank.syllable_count('hopeless').should == 2
      @readability_blank.syllable_count('hopelessly').should == 3
      @readability_blank.syllable_count('careful').should == 2
      @readability_blank.syllable_count('carefully').should == 3
      @readability_blank.syllable_count('stuffy').should == 2
      @readability_blank.syllable_count('thistle').should == 2
      @readability_blank.syllable_count('teacher').should == 2
      @readability_blank.syllable_count('unhappy').should == 3
      @readability_blank.syllable_count('ambiguity').should == 5
      @readability_blank.syllable_count('validity').should == 4
      @readability_blank.syllable_count('ambiguous').should == 4
      @readability_blank.syllable_count('deserve').should == 2
      @readability_blank.syllable_count('blooper').should == 2
      @readability_blank.syllable_count('scooped').should == 1
      @readability_blank.syllable_count('deserve').should == 2
      @readability_blank.syllable_count('deal').should == 1
      @readability_blank.syllable_count('death').should == 1
      @readability_blank.syllable_count('dearth').should == 1
      @readability_blank.syllable_count('deign').should == 1
      @readability_blank.syllable_count('reign').should == 1
      @readability_blank.syllable_count('bedsore').should == 2
      @readability_blank.syllable_count('anorexia').should == 5
      @readability_blank.syllable_count('anymore').should == 3
      @readability_blank.syllable_count('cored').should == 1
      @readability_blank.syllable_count('sore').should == 1
      @readability_blank.syllable_count('foremost').should == 2
      @readability_blank.syllable_count('restore').should == 2
      @readability_blank.syllable_count('minute').should == 2
      @readability_blank.syllable_count('manticores').should == 3
      @readability_blank.syllable_count('asparagus').should == 4
      @readability_blank.syllable_count('unexplored').should == 3
      @readability_blank.syllable_count('unexploded').should == 4
      @readability_blank.syllable_count('CAPITALS').should == 3
    end

    it "should calculate average syllables per word" do
      Readability.new('and then there was
one').average_syllables_per_word.should == 1
      Readability.new('because special ducklings deserve
rainbows').average_syllables_per_word.should == 2
      Readability.new('and then there was one because special
ducklings deserve rainbows').average_syllables_per_word.should ==
1.5
    end

    it "should count words correctly" do
      Readability.new('The quick brown fox jumped over the lazy
dog').word_count.should == 9
      Readability.new('The quick brown fox jumped over the lazy
dog.').word_count.should == 9
      Readability.new('The quick brown fox jumped over the lazy dog.
').word_count.should == 9
      Readability.new(' The quick brown fox jumped over the lazy dog.
').word_count.should == 9
      Readability.new(' The  quick brown fox jumped over the lazy dog.
').word_count.should == 9
      Readability.new('Yes. No.').word_count.should == 2
      Readability.new('Yes.No.').word_count.should == 2
      Readability.new('Yes.No.').word_count.should == 2
      Readability.new('Yes . No.').word_count.should == 2
      Readability.new('Yes - No. ').word_count.should == 2
    end

    it "should get percentage of words with three syllables" do
      Readability.new('there is just one word with three syllables in
this sentence').percentage_words_with_three_syllables.round.should ==
9
      Readability.new('there are no valid words with three Syllables
in this sentence').percentage_words_with_three_syllables.round.should
== 9
      Readability.new('there is one and only one word with three or
more syllables in this long boring sentence of twenty
words').percentage_words_with_three_syllables.round.should == 5
      Readability.new('there are two and only two words with three or
more syllables in this long sentence of exactly twenty
words').percentage_words_with_three_syllables.round.should == 10
      Readability.new('there is Actually only one valid word with
three or more syllables in this long sentence of Exactly twenty
words').percentage_words_with_three_syllables(false).round.should == 5
      Readability.new('no long words in this
sentence').percentage_words_with_three_syllables.round.should == 0
      Readability.new('no long valid words in this sentence because
the test ignores proper case words like this
Behemoth').percentage_words_with_three_syllables(false).round.should
== 0
    end

    it "should count letters" do
      Readability.new('a').letter_count.should == 1
      Readability.new('').letter_count.should == 0
      Readability.new('this sentence has 30 characters, not including
the digits').letter_count.should == 46
    end

    it "should count sentences" do
      Readability.new('This is a sentence').sentence_count.should == 1
      Readability.new('This is a sentence.').sentence_count.should ==
1
      Readability.new('This is a sentence!').sentence_count.should ==
1
      Readability.new('This is a sentence?').sentence_count.should ==
1
      Readability.new('This is a sentence..').sentence_count.should ==
1
      Readability.new('This is a sentence. So is
this.').sentence_count.should == 2
      Readability.new("This is a sentence. \n\n So is this, but this
is multi-line!").sentence_count.should == 2
      Readability.new('This is a sentence,. So is
this.').sentence_count.should == 2
      Readability.new('This is a sentence!? So is
this.').sentence_count.should == 2
      Readability.new('This is a sentence. So is this. And this one as
well.').sentence_count.should == 3
      Readability.new('This is a sentence - but just
one.').sentence_count.should == 1
      Readability.new('This is a sentence (but just
one).').sentence_count.should == 1
    end

    it "should calculate average words per sentence" do
      Readability.new('This is a
sentence').average_words_per_sentence.should == 4
      Readability.new('This is a
sentence.').average_words_per_sentence.should == 4
      Readability.new('This is a sentence.
').average_words_per_sentence.should == 4
      Readability.new('This is a sentence. This is a
sentence').average_words_per_sentence.should == 4
      Readability.new('This is a sentence. This is a
sentence.').average_words_per_sentence.should == 4
      Readability.new('This, is - a sentence . This is a sentence.
').average_words_per_sentence.should == 4
      Readability.new('This is a sentence with extra text. This is a
sentence. ').average_words_per_sentence.should == 5.5
      Readability.new('This is a sentence with some extra text. This
is a sentence. ').average_words_per_sentence.should == 6
    end

    describe "test indices directly" do
      before(:each) do
        @str_a = 'This. Is. A. Nice. Set. Of. Small. Words. Of. One.
Part. Each.'
        @str_b = 'The quick brown fox jumped over the lazy dog.'
        @str_c = 'The quick brown fox jumped over the lazy dog. The
quick brown fox jumped over the lazy dog.'
        @str_d = "The quick brown fox jumped over the lazy dog. \n\n
The quick brown fox jumped over the lazy dog."
        @str_e = 'The quick brown fox jumped over the lazy dog. The
quick brown fox jumped over the lazy dog'
        @str_f = 'Now it is time for a more complicated sentence,
including several longer words.'
        @str_g = 'Now it is time for a more Complicated sentence,
including Several longer words.'
      end

      it "should calculate flesch-kincaid reading ease" do
        Readability.new(@str_a).flesch_kincaid_reading_ease.should ==
121.2
        Readability.new(@str_b).flesch_kincaid_reading_ease.should ==
94.3
        Readability.new(@str_c).flesch_kincaid_reading_ease.should ==
94.3
        Readability.new(@str_d).flesch_kincaid_reading_ease.should ==
94.3
        Readability.new(@str_e).flesch_kincaid_reading_ease.should ==
94.3
        Readability.new(@str_f).flesch_kincaid_reading_ease.should ==
50.5
      end

      it "should calculate flesch-kincaid grade level" do
        Readability.new(@str_a).flesch_kincaid_grade_level.should ==
-3.4
        Readability.new(@str_b).flesch_kincaid_grade_level.should ==
2.3
        Readability.new(@str_c).flesch_kincaid_grade_level.should ==
2.3
        Readability.new(@str_d).flesch_kincaid_grade_level.should ==
2.3
        Readability.new(@str_e).flesch_kincaid_grade_level.should ==
2.3
        Readability.new(@str_f).flesch_kincaid_grade_level.should ==
9.4
      end

      it "should calculate Gunning-Fog Score" do
        Readability.new(@str_a).gunning_fog_score.should == 0.4
        Readability.new(@str_b).gunning_fog_score.should == 3.6
        Readability.new(@str_c).gunning_fog_score.should == 3.6
        Readability.new(@str_d).gunning_fog_score.should == 3.6
        Readability.new(@str_e).gunning_fog_score.should == 3.6
        Readability.new(@str_f).gunning_fog_score.should == 14.4
        Readability.new(@str_g).gunning_fog_score.should == 8.3
      end

      it "should calculate coleman-liau index" do
        Readability.new(@str_a).coleman_liau_index.should == 3.0
        Readability.new(@str_b).coleman_liau_index.should == 7.7
        Readability.new(@str_c).coleman_liau_index.should == 7.7
        Readability.new(@str_d).coleman_liau_index.should == 7.7
        Readability.new(@str_e).coleman_liau_index.should == 7.7
        Readability.new(@str_f).coleman_liau_index.should ==
13.6
      end

      it "should calculate smog index" do
        Readability.new(@str_a).smog_index.should == 1.8
        Readability.new(@str_b).smog_index.should == 1.8
        Readability.new(@str_c).smog_index.should == 1.8
        Readability.new(@str_d).smog_index.should == 1.8
        Readability.new(@str_e).smog_index.should == 1.8
        Readability.new(@str_f).smog_index.should ==
10.1
      end

      it "should calculate automated readability index" do
        Readability.new(@str_a).automated_readability_index.should ==
-5.6
        Readability.new(@str_b).automated_readability_index.should ==
1.9
        Readability.new(@str_c).automated_readability_index.should ==
1.9
        Readability.new(@str_d).automated_readability_index.should ==
1.9
        Readability.new(@str_e).automated_readability_index.should ==
1.9
        Readability.new(@str_f).automated_readability_index.should ==
8.6
      end

      it "should index first paragraph of Moby Dick correctly" do
        str =<<-ENDL
          Call me Ishmael. Some years ago - never mind how long
precisely - having little or no money in my purse, and
          nothing particular to interest me on shore, I thought I
would sail about a little and see the watery part of
          the world. It is a way I have of driving off the spleen, and
regulating the circulation. Whenever I find myself
          growing grim about the mouth; whenever it is a damp, drizzly
November in my soul; whenever I find myself
          involuntarily pausing before coffin warehouses, and bringing
up the rear of every funeral I meet; and especially
          whenever my hypos get such an upper hand of me, that it
requires a strong moral principle to prevent me from
          deliberately stepping into the street, and methodically
knocking people's hats off - then, I account it high time
          to get to sea as soon as I can. This is my substitute for
pistol and ball. With a philosophical flourish Cato
          throws himself upon his sword; I quietly take to the ship.
There is nothing surprising in this. If they but knew
          it, almost all men in their degree, some time or other,
cherish very nearly the same feelings towards the ocean with me.
        ENDL

        readability = Readability.new(str)

        readability.letter_count.should == 884
        readability.word_count.should == 201
        readability.total_syllables.should == 304
        readability.sentence_count.should == 8
        readability.words_with_three_syllables.should == 23

        readability.flesch_kincaid_grade_level.should == 12.1
        readability.flesch_kincaid_reading_ease.should == 53.4
        readability.gunning_fog_score.should == 14.2
        readability.coleman_liau_index.should == 10.1
        readability.smog_index.should == 8.9
        readability.automated_readability_index.should == 11.8
      end

      it "should index a Kipling poem correctly" do
        str =<<-ENDL
          If you can keep your head when all about you
          Are losing theirs and blaming it on you,
          If you can trust yourself when all men doubt you
          But make allowance for their doubting too,
          If you can wait and not be tired by waiting,
          Or being lied about, don't deal in lies,
          Or being hated, don't give way to hating,
          And yet don't look too good, nor talk too wise:

          If you can dream - and not make dreams your master,
          If you can think - and not make thoughts your aim;
          If you can meet with Triumph and Disaster
          And treat those two impostors just the same;
          If you can bear to hear the truth you've spoken
          Twisted by knaves to make a trap for fools,
          Or watch the things you gave your life to, broken,
          And stoop and build 'em up with worn-out tools:

          If you can make one heap of all your winnings
          And risk it all on one turn of pitch-and-toss,
          And lose, and start again at your beginnings
          And never breath a word about your loss;
          If you can force your heart and nerve and sinew
          To serve your turn long after they are gone,
          And so hold on when there is nothing in you
          Except the Will which says to them: "Hold on"

          If you can talk with crowds and keep your virtue,
          Or walk with kings - nor lose the common touch,
          If neither foes nor loving friends can hurt you;
          If all men count with you, but none too much,
          If you can fill the unforgiving minute
          With sixty seconds' worth of distance run,
          Yours is the Earth and everything that's in it,
          And - which is more - you'll be a Man, my son
        ENDL

        readability = Readability.new(str)

        readability.letter_count.should == 1125
        readability.word_count.should == 292
        readability.total_syllables.should == 338
        readability.sentence_count.should == 1
        readability.words_with_three_syllables.should == 6