Running git on top file based storage would also be an interesting project. There is a proprietary commercial implementation of a similar idea from Caringo call

Running git on top file based storage would also be an interesting project. There is a proprietary commercial implementation of a similar idea from Caringo called CFS http://www.caringo.com/products_cfs.html http://www.caringo.com/products_cfs.html. An opensource version based on git would be nice.