Yeah, FlockDB (https://github.com/twitter/flockdb https://github.com/twitter/flockdb) comes to mind. I think Titan (https://github.com/thinkaurelius/titan https

Yeah, FlockDB (https://github.com/twitter/flockdb https://github.com/twitter/flockdb) comes to mind. I think Titan (https://github.com/thinkaurelius/titan https://github.com/thinkaurelius/titan) should / will be able to handle this too.