DragonFly is an operating system and environment designed to be the logical continuation of the FreeBSD-4.x OS series. These operating systems belong in the same class as Linux in that they are based on UNIX ideals and APIs. DragonFly is a fork in the path, so to speak, giving the BSD base an opportunity to grow in an entirely new direction from the one taken in the FreeBSD-5 series.
DragonFly BSD 1.4 has been released: "1.4 is our third major DragonFly release. This release represents a significant milestone in our efforts to improve the kernel infrastructure. DragonFly is still running under the Big Giant Lock, but this will probably be the last release where that is the case. The greatest progress has been made in the network subsystem. The TCP stack is now almost fully threaded (and will likely be the first subsystem we remove the BGL from in coming months). The TCP stack now fully supports the SACK protocol and a large number of bug and performance fixes have gone in, especially in regard to GigE performance over LANs
DragonFly BSD is a fork of FreeBSD 4.x series, representing a logical continuation of the branch that proved itself to be one of the most stable and reliable FreeBSD releases ever built.