Phing-ext-gittasks is a project mainly written in PHP, it's free.
Extra git tasks for phing (extending the GitBaseTask provided by recent phing releases)
Additional git related tasks for the phing build tool.
Phing currently comes with several tasks for interacting with git repositories, but it also lacks some that I have a need for. Thus, I am implementing them myself by extending phing's provided GitBaseTask class. I've implemented them more or less, and have submitted them to the phing maintainers for inclusion in a future release.
Installing these extra tasks is fairly straightforward, but first you need to locate your phing installation. In my case, I installed phing via pear, which was installed as part of Zend Server CE; my phing installation is therefore located in /usr/local/zend/share/pear/phing. Simply copy the Git*Task.php files from this repository into $PHING/tasks/ext/git/ and define them in your build.xml file as taskdef entries (similar to what is done in this repo).