It's called Liaise. Liaise is an Outlook add-in that automatically understands action items as you enter them in e-mail, tracks them, and helps you get them resolved on schedule.
That might sound a bit like science fiction, but I've tried it, and it works surprisingly well. As you type an e-mail, it identifies action items, who they're assigned to, and when they're due, all just from the context of the message. If it gets something wrong, it's easy to correct on the fly. These action items appear in your calendar to help you stay on top of your tasks. And if you schedule a meeting with people to whom tasks are assigned, you can see all the issues in the meeting notes.
Liaise is impressive -- it has the kind of business intelligence baked in that reminds us it's very nearly 2010, the year of science fiction-y stuff like alien contact. It's currently free and in public beta. The only downside? It doesn't work with Office 2010, which is too bad if you're currently beta testing the next version of Office.
Want to see it in action? Be sure to watch the video.