http://git-scm.com/
Homepage for TIG:
http://jonas.nitro.dk/tig/
Download:
Approx 6mb - GIT:
http://www.datafilehost.com/download-953dfcd2.html
To use GIT, open up 'terminal' and enter the details eg
The contents will end up in your Home/Root folder
git clone git://github.com/xbmc/xbmc.git