So I'd like to stress that while it really came together in just about ten days or so, it wasn't like it was some kind of mad dash of coding. The actual amount of that early code is actually fairly small, it all depended on getting the basic ideas right. And that I had been mulling over for a while before the whole project started. I'd seen the problems others had. I'd seen what I wanted to avoid doing.

http://www.linux.com/news/featured-blogs/185-jennifer-cloer/821541-10-years-of-git-an-interview-with-git-creator-linus-torvalds

The source code manager to build git was... git.