Sites listing Ruby on Rails challenges

[Jason Hsu, Rubyist]

Is there a site that lists Ruby on Rails challenges to try?  I think I found a mention of such a site once, but I forgot the URL, and I haven't been able to find this site.  I don't mean tutorials like railstutorial.org or railsbridge.org but sites that provide coding challenges to try - the web development equivalent of something like "Hello World" but more challenging.

This wouldn't be a major pet project - just some smaller projects that would give me a chance to apply what I've learned about MVC, testing, etc.  Such a challenge would cover areas that my pet projects do not.