Unfortunately offline as of 2014/05/15 with very little reason given by its maintainers. The new place to be is RubyGems.
A lot of "finished" projects (TrollOp?, an options parser, comes to mind) never made the jump, and so now their documentation is forever lost to the sands of time (or Google or your favorite archive site)
The SourceForge concept, with a pleasant RubyLanguage focus. 4,220 registered projects, 20,697 registered developers as of 2007/9/30.