In a short time since its creation, Git has managed to become one of the most popular version control systems. Git was originally created by Linus Torvalds as a version control system for the Linux kernel, however since then has found broad acceptance in the open source community. Especially thanks to services such as GitHub that make it incredible easy (and free) to host open source project, and to fork / clone / merge them.
Now Google has introduced support for Git has a version control option for projects hosted on Google Code. Previously they only supported Subversion (a centralized VCS), and Mercurial (a distributed VCS) for version control. Initially Google has only implemented Mercurial since it was easier to migrate to from Subversion, and had better HTTP performance characteristics and protocol compared to Git. However they feel Git has improved a lot since then.
Like their implementation of Mercurial, their Git implementation is based on Python as well. For this they have used an open source project called Dulwich, which is an implementation of Git in Python. Git was originally written mostly in C.
Since Google added support for creating project clones, and tracking / merging these clones, it has become a pretty good alternative for GitHub. However unlike GitHub, Google Code only allows hosting open source projects for free, they have not commercial plans for closed source software like GitHub does, so the project development has to be open from the start.