The ROT is the running object table in Windows. It lets you know which COM objects still have a ref count of higher than zero. There is a tool, called ROT viewer (IROTVIEW application) that gets installed with visual studio. If you look up the GUIDs that still have ref counts, you can reverse look them up in the registry to see what is running. So if you launch an app that uses COM components (Excel, Word, Powerpoint, etc), you can turn on the ROT viewer and see that the GUID for Excel.Application (or Word.Application, or what not)is running.

What does this mean? That means all of those arcane numbers in the registry look up to being different applications with COM components.