Rather small one, but if you work with ActiveX controls and play around with manifest files, it's pretty handy.
It's a registry script that adds a couple of options to the right mouse button popup menu in Windows Explorer when you're on an ActiveX or related files (e.g., type library).
If you want to be able to register / unregister an ActiveX control with a couple of mouse clicks, it's great.
Chris has quite a few other utilities on that page as well. The UrlRun and the XML validator look intriguing, but I haven't tried them yet.