Gmail-Users - join
Talk about Gmail, good or bad.
Low activity, 17936 members, moderated, restricted

Google Calendar Help (Archived) - join
Welcome to the Google Calendar Help Forum Archive! Please note that this forum is only an archive and you can no longer post questions here. Please see our new forum here: http://www.google.com/support/forum/p/Calendar?hl=en
44698 members, restricted

GMusers- GMail Beta & Beyond - join
A core group of GMail users who expect to be using GMail through beta and beyond. The list is moderated. There are multiple moderators in order to preserve diversity of opinion and a smooth flow of posts. GMusers is open and globally inclusive. You do not need a GMail account to join.
Low activity, 3195 members, moderated, restricted