GitG is GNOME's GitX clone that's written with a GTK+ interface and designed to be a small/fast tool for visualizing Git history and actions. While not symbolized by the name, GitG 0.3.1 is the first release since the code's major rewrite and there's been many changes.
GitG has been rewritten in Vala rather than C, which according to the developers has eased developments. The Vala-based GitG is now also using the libgit2 library rather than calling out Git commands directly. The GitG interface has also been improved and is now in compliance with the GNOME 3 applications interface guidelines.
Rewriting the code-base has led to a temporary loss of features, including known regressions of push/pull branch support, create/rename/delete branches and tags, and basic remote branch management. Those features are expected to come back in future versions.
More details on GitG 0.3.1 can be found via their mailing list announcement from this weekend.