As you can imagine, a company full of great developers such as Microsoft has a bunch of folks that crank out a lot of tools and utilities in their "spare" time. One of those that has been extremely popular internally is VMRCPlus, an alternate interface for managing and interacting with Virtual Server 2005 hosts and guests. I'm a big fan of Virtual Server and use it daily. Like many, I've never been a big fan of the Web UI. VMRCPlus fills that gap by providing a much easier to use and more function UI for Virtual Server. Fortunately, this internal project has matured enough that it is being released to the public with the caveat that it is not officially supported by Microsoft. That said, Microsoft folks are very heavy users of Virtual Server and VMRCPlus is utilized by many of them and has been around for a while so it is pretty mature. It is also an extreme example of how much can be done using the documented Virtual Server COM APIs.
Keith has a good feature list and a link to download here.
Arlindo has some screenshots here.