It's an add-on to the NT/2K/XP Task Manager that let's you do things that other stand-alone task managers do. It displays icons for processes that have them, tells you what files, modules, handles, and windows a process has open. Also let's you close handles, files, windows, and unload modules. And let's you search by file or module to find out what processes have them open/loaded.
Very yum. :D