A Windows driver implementation of btrfs, so you can use it from a windows system.

I believe it is still (highly?) experimental so do not use it for sensitive and important files, in fact best use it on a test system with disposables drives first.

But I have seen some people use it to have e.g. windows and steamos have access to the same btrfs drive for games so they don't have to duplicate the 100+GB game files for switching systems, quite clever.