this addon allows to store different versions of whole .blend files inside a Git repo. It is able to commit and checkout currently saved blends from within blender. There you can also view a brief history of the blend. Basic support for branches is there too, although i know diffing binary files like text files does not make much sense at all. The addon is more intended to save a linear history of different blend versions from within blender.
Note: to enable versioning, you must first save the blend. Best practice is to do this in a dedicated subdirectory, because git repos are automatically initialized there by the addon.