If you haven't heard, RubyForge will be closing down for good on May 15th this year. This is truly the end of an era.
RubyForge began on July 22, 2003. You can see the original announcement here. The kind folks at InfoEther (namely Rich Kilmer and Tom Copeland) had given a nascent Ruby community a place to host projects, not just list them as the old RAA had done.
Based on the GForge code (mostly popularized by SourceForge), it didn't take long for it to catch on in the Ruby community. Not only did it provide hosting, but you could do bug tracking, manage mailing lists, post news announcements, set your own tasks and integrate your version control with it. There were also general areas where you could post code snippets, and you could even see some download statisics. It was fantastic, and soon we had a real competitor for Perl's CPAN.
Some of the most well known libraries in the Ruby community would be started (or soon migrated) there, including rubygems and rake. My own libraries, including the win32utils libraries, would also be hosted there. All hosted there since 2003.
Alas, all good things come to an end. There were several reasons for this, but first and foremost was the rise of git and github. Many people felt RubyForge had become too old school - many of its features often went unused - and they preferred the github.com interface. On top of that it's somewhat difficult to maintain. Being a PHP app meant Ruby programmers couldn't really help with any enhancements or fixes and, although other folks chipped in where they could, that left mostly just Tom to handle issues.
And so, RubyForge will close down this year, having hosted over 9,600 projects with over 100,000 registered users. But more than that, I believe that RubyForge was responsible for helping to popularize a relatively young language and for bringing together Ruby programmers together in the spirit of cooperation. It was, in my opinion, the first "social programming" site for Rubyists around the world.