Arbitrary commit diffs have been in Github since March 2010 [1]. The Overview is exactly like what Redmine and GitLab call 'Activity' [2]. Github has Activity in a different manner, through notifications and the News Feed. These are useful features, but they are not innovative.
[1] https://github.com/blog/612-introducing-github-compare-view
[2] http://www.redmine.org/projects/redmine/activity