It's my own product/service. I have my own diff, commit and source viewer. With my setup, the only time that you would use GitHub is to make comments.

Here are some additional screen shots of the other tools.

Unified diff view

http://6b507fb6377c7b2ce0ed-f6f6a52addfcf546a4b633fce1dd247e...

Side-by-side diff view

http://6b507fb6377c7b2ce0ed-f6f6a52addfcf546a4b633fce1dd247e...

Blame source view with timeline highlighting

http://6b507fb6377c7b2ce0ed-f6f6a52addfcf546a4b633fce1dd247e...

Creating your own custom diff view.

http://6b507fb6377c7b2ce0ed-f6f6a52addfcf546a4b633fce1dd247e...

Commit view

http://6b507fb6377c7b2ce0ed-f6f6a52addfcf546a4b633fce1dd247e...

Edit.

Added source tree screenshot

http://6b507fb6377c7b2ce0ed-f6f6a52addfcf546a4b633fce1dd247e...