How can I add a messaging sub-app to my Rails 3 application?

I basically just want users to be able to interact with ea开发者_C百科ch other, thread style. Is there a gem or a plugin that will accomplish this for me, or must I roll my own?

ryan bates has a screen cast, http://railscasts.com/episodes/262-trees-with-ancestry. He uses the ancestry gem to create a threaded comment system.