Most Ruby developers are familiar with Git by now. (If you're not: it's a distributed version control system that was created in 2005 by Linus Torvalds for Linux kernel development). Within the last year almost every Ruby-based open-source project has switched to Git (including Rails itself). And in fact they're almost all hosted on Github!
At first I found it funny that even though they were moving to a distributed version control system, everyone decided to keep their repositories in the exact same place. Being distributed, a Git repository doesn't need to be hosted unless you're sharing it. You can publish it easily on any web server, and RubyForge (which has always been the most popular place to host Ruby projects) supports git.
But after playing with it a bit I can see why everyone is choosing Github. For one thing they got the project hosting part right, with a simple clean UI and cool features like an API and hooks for all kinds of services.
But the really cool thing about Github is that it provides a social environment. You can watch projects as you'd expect, but you can also follow people, send them messages, and easily send them pull requests (to integrate changes you've made). It's great for discovering interesting and new projects: just follow friends and people whose work you like to see what they're watching, creating and forking.
Now that EC2 on Rails is on Github it's more likely that other people will want to build it themselves so I'll try to make that easier with a one- step script at the root of the project. Feel free to fork it, implement changes and send me patches or pull requests.
And find me on Github!