The other day I discovered this really cool resource for finding stuff
on the web. It's called Google. I don't know...maybe you've heard of
it? 
http://www.google.com/search?client=safari&rls=en&q=open+source+rails+projects&ie=UTF-8&oe=UTF-8
The number one result: http://wiki.rubyonrails.org/rails/pages/OpenSourceProjects