Microsoft introduced in Windows 95 the registry database, to gather all parameters of anykind.
This big package grows as a monster when installing and uninstalling software.
With this program, Microsoft tries to make some corrections by cleaning the uneseless information. The program is often to launch 3 or 4 times to finish its corrections.
There are too many many things in the registry
Strangely and clumsily, the program works as soon as it is launched... Happily a .reg file is generated, to verify the modifications, eventually undo it. The content of the file would be automatically opened, it would have been better... Really not ergonomic...
To download it, go to the ZDNet site, and do a search on the word RegClean.