A PC Decrapifier is a program which removes unwanted files from your PC. The program will scan the applications installed on your PC, and any software or system component that you might not want on your PC. This is especially useful for people who delete their systems often or use very large, high end graphics cards. Most of the time, if you do delete an application in the removal process is to restart your computer. If you have one of these programs running, it will never restart and will always remove the application, meaning you'll never get rid of the applications that are no longer being used. This is a major problem, because it leads to data loss, because the computer will be unable to find any file that was deleted. Fortunately, with a good program, you can fix this problem.
Free programs will scan the registry database and tell you if you have any unwanted program that was removed by accident. I recommend the application called "RegCure", because it works very well, and it has been around for a long time. The application is able to remove errors, settings, and errors inside the registry. When you uninstall a program, it will generally remove the settings and other information related to that program. So you want to be able to keep the registry free of errors and missing information, to make sure that your PC runs smoothly.
Another free program that works well is called "Dllcleaner". This can also be found on the internet, but I would suggest using the downloadable version. This is because the program is designed specifically to clean up the dll file, which is a software library which Windows uses to load important files into memory. If you have corrupted dll files, then your computer will take a long time to run, leading to slower computer performance.