Here's a landing page from Trello which made me sign up: http://trello.com/. It tells me why I need them, what they do, and, lo and behold, a video demo right on top.
I signed up with trello right away. I haven't used them since, but at least I signed up. &! just makes me go ?!.
In essence, everyone makes short lists of what they're really working on that day (or near future) then marks what they're actually doing as active.
Then you have a live dashboard view of your full team, can see each other's lists, and add each other. Throw in team chat.
But it's more than the features. Here's the philosophy: http://blog.andbang.com/post/6038837039/the-philosophy