Speaking of Worm group activities, Wildbow was, at one point, in the process of making a tabletop RPG based on Worm.
The mechanical side of things was, as far as I know, never finished, but the mechanics for 'choosing' your powers were, and are quite cool. Let me see if I can find that link...
Here we go. Weaver Dice
Ah, and here's a newer version. Weaverdice (character creation)
One thing I've wanted to try for a while is taking the Weaverdice character creation method for a group, and then the group works together to build and play those characters in HERO 6E (if you want to get really granular) or Masks (much easier, but also much more 'broad-strokes') or something.