One of the things I like about it is that as well as the different project groups that can be set up, it also features a central area where everyone can share stuff, ask questions and so on. So it combines the project management of tools like Huddle with some of the more social features of Yammer.
Here’s a video that explains it a little more:
If you’re in the market for one of these tools – and who isn’t?!? – then it could well work for you. There’s a free option so you can trial it with a small group first.