How do I compare cloned github projects?

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http://www.linuxquestions.org – Github makes it very easy to clone an existing project so you can make your own version the way you want to. But I don't see any way to easily compare a project to a clone to see what's different. Consider these two projects as an example: github.com/offbytwo/git-hg and github.com/cosmin/git-hg I could clone them both locally and do a file-by-file compare, but for big projects that would be laborious. Does anyone have any trick or insight for a quicker solution? (HowTos)