Reiser4

Reiser4 is a computer file system, successor to the ReiserFS file system, developed from scratch by Namesys and sponsored by DARPA as well as Linspire. Reiser4 was named after its former lead developer Hans Reiser. As of 2015, the Reiser4 patch set is still being maintained, but according to Phoronix, it's unlikely to be merged into mainline Linux without corporate backing.