Which Programs Are Safe To Uninstall To Free Up Room On My Hard Drive?

A lot of program's identities and functions are obvious, especially ones I've installed, but there are some on my hard drive that I'd like to uninstall, but I don't want to risk screwing anything up. Rather than Google each one individually, is there a program that can help me figure out what is *necessary* versus what is superfluous?
 
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