GNU Hurd

GNU Hurd is a multiserver kernel with the goal of providing users with as much freedom to do as they wish with the GNU operating system as possible. It was initially intended to provide a free alternative to Unix (GNU stands for "GNU's Not Unix"). The Hurd was the intended implementation of the GNU operating system before Linux became the kernel of choice for GNU users. The current goal of the Hurd project is:
[T]o create a general-purpose kernel suitable for the GNU operating system, which is viable for everyday use, and gives users and programs as much control over their computing environment as possible.
The Hurd kernel consists of a microkernel that provides basic kernel services and a collection (or "herd") of servers / daemons that provided services that are beyond basic. This design was meant to provide developers with freedom that Unix and other Unix-like operating systems did not. For example, this design allows developers to program servers in languages other than the one used by the kernel. GNU Mach currently is the microkernel being used in the Hurd.
Richard Stallman created the GNU project in 1983 and founded the Free Software Foundation (FSF) in 1985 in order to fund and promote the development of free software and GNU. By the early 1990's, the GNU toolchain and other components besides the kernel were completed. Work began the Hurd in 1990. Stallman decided to use Carnegie Mellon University's Mach microkernel as the basis for the Hurd microkernel.
In 1991, Linus Torvalds released the Linux kernel, and free software enthusiasts ported GNU's completed components to the Linux kernel in order to create GNU/Linux. NetBSD and FreeBSD were released a couple of years later, yet the Hurd was not in a functional state. Due to the presence of functioning alternatives, interest in the Hurd waned. As the FSF moved away from GNU development and more towards free software activism, Debian became more involved in the Hurd's development.