Beast is a nice, light-weight forum written in Rails. From what I can gather, the overall goal is to make something work with only 500 lines of code, and I think that could happen with this. It is open source, and can easily be checked out
I did check it out and I have to say that I’m impressed. It is using the rails edge and is trying out some of the REST(representational state transfer)ful stuff all the while adhering to the philosophies of CRUD(create, read, update, delete). I have wanted to look into a good example of a rails project using REST, and this code base is great for that. What’s more is that it’s not very difficult to wrap your head around all of the code of the site, due to the small code base and nice abstraction of the code.