Sites listing Ruby on Rails challenges

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.