alt.math.recreational - join
Low activity, 492 subscribers, Usenet

rec.puzzles.crosswords - join
Making and playing gridded word puzzles.
Medium activity, 296 subscribers, Usenet

sci.math - join
Mathematical discussions and pursuits.
High activity, 10979 subscribers, Usenet

alt.math.undergrad - join
Medium activity, 1404 subscribers, Usenet

comp.programming - join
Programming issues that transcend languages and OSs.
High activity, 3731 subscribers, Usenet

alt.brain.teasers - join
Low activity, 214 subscribers, Usenet

geometry.puzzles - join
Recreational Geometry Problems. (Moderated)
Low activity, 126 subscribers, Usenet

ultimate hard puzzles - join
This group is intended to be the most powerfull puzzle collection group in the world. Any trivial puzzle or any subject except puzzles will be erased.
Low activity, 55 members

Puzzle - join
A group devoted to interesting news and items in the world of puzzles.
Low activity, 192 members, moderated

alt.math - join
Low activity, 734 subscribers, Usenet