37Signals makes a lot of great web-based applications. They just released a new one, called Writeboard, recently. The concept, as with their other apps, is simple. Here you have a web-based, collaborative text editor, complete with some simple versioning, commenting, and diffing (i.e. the ability to compare any two versions for differences). The docs are password protected and there’s an invite mechanism for asking your collaborators to take a look at the doc. They even include some really simple HTML-ish formatting tags for doing hyperlinks, headings, and lists. When you’re done with it, you can drop it into your word processor and put on the finishing touches. That’s all there is to it. It’s all very basic stuff, but never implemented better.