Have you looked at Git-PHP? http://code.google.com/p/git-php/
There is also:
glip
glip, a git library in PHP, enables your PHP scripts to access git repositories. Written in pure PHP5, it works without even having git installed, thus making it the ideal git library to use with your el-cheapo web hosting service.
GitPHP
GitPHP is a web frontend for git repositories. It emulates the look of standard gitweb, but is written in PHP and makes use of Smarty templates for customization. It has a couple extras, including syntax highlighting through the GeSHi PHP class and project category support. It works with standard git as well as msysgit on Windows.