Writeboard and WriteRoom are a killer combo. If you don't know, Writeroom is a full-screen, distraction-free writing environment for Mac. When you use it, obstacles fade away. It's just you and your text.
Combine that with the version control of Writeboard and you've got a great writing platform. You have no choice but to write something or get up and do something else. And you've got an easy way to collaborate, track changes, and revert to earlier versions. Give it a whirl.
