HAMMER filesystem adds letters to Sun's ZFS which supposed to be the "last word in filesystems"
DragonFlyBSD is a fork of the FreeBSD 4.x series which was made by Matthew Dillon. His intention was to create an operating system being suitable for enhancement with technologies focused on clustering, multi-core/CPU architectures (SMP) and concurrency. One of the main sub-projects of DragonFlyBSD is the development of an accordant filesystem called HAMMER. As the operating system itself the HAMMER filesystem is going to be highly scalable filesystem containing all(?) features of ZFS as well as some ground-breaking additional features like the built-in clustering facility. A nice comparison between ZFS and HAMMER emphasizes also its resource frugality. With HAMMER's infinite snapshot capability which keeps track of every change to a file, it is even possible to make source code repository systems like CVS, SVN and Git obsolete. According to Matthew Dillons statement regarding Michael Neumann's article "HAMMER vs. ZFS" he is "making good progress" building HAMMER.