program that finds any cruft built up on your system

 cruft is a program to look over your system for anything that shouldn't
 be there, but is; or for anything that should be there, but isn't.
 .
 It bases most of its results on dpkg's database, as well as a list of
 `extra files' that can appear during the lifetime of various packages.
 .
 cruft is still in pre-release; your assistance in improving its accuracy
 and performance is appreciated.