The GNU project has released GNU Hurd 0.9, GNU Mach 1.8, and GNU MIG 1.8. Hurd has been in development for a long time, and is supposed to - eventually - be the official kernel for the GNU operating system, a role currently unofficially filled by the Linux kernel. GNU Mach is a little bit different.
GNU Mach is the GNU distribution of the Mach microkernel, upon which a GNU Hurd system is based. The microkernel provides an Inter Process Communication (IPC) mechanism that the Hurd uses to define interfaces for implementing in a distributed multi-server fashion the services a traditional operating system kernel provides.