If you like Twitter and the idea that you can easily follow along with what your friends and colleagues are doing all day, you might like the new Prologue WordPress Theme.
The theme skins your blog to look like a set of Twitter updates, and the “what are you doing now?” form for posting an update is conveniently located on the top of the home page.
This setup would be perfect for small groups or distributed teams who want to keep track of each other. You could password-protect the blog if you want to limit who can view the posts. In the same way, you limit those that could post updates by having only registered users be able to post updates.
The Prologue team has already released an update that improves the layout of the updates and includes Gravatar support.