TortoiseGit is a Windows Shell Interface to Git and based on TortoiseSVN. It's open source and can fully be build with freely available software.
Since it's not an integration for a specific IDE like Visual Studio, Eclipse or others, you can use it with whatever development tools you like, and with any type of file. Main interaction with TortoiseGit will be using the context menu of the Windows explorer.
It is developed under the GPL. Which means it is completely free for anyone to use, including in a commercial environment, without any restriction. The source code is also freely available, so you can even develop your own version if you wish to.