GIT is a “directory content manager” designed to handle absolutely massive projects with speed and efficiency, and the release of the 2.6.12 and (soon) the 2.6.13 version of the Linux kernel would indicate that it does this task well.
GIT falls into the category of distributed source code management tools, similar to Arch or Darcs (or, in the commercial world, BitKeeper). Every GIT working directory is a full-fledged repository with full revision tracking capabilities, not dependent on network access to a central server.