GNU Hurd – microkernel and part of GNU Project.
Hurd means “Hird of Unix-Replacing Daemons”,
Hird – “Hurd of Interfaces Representing Depth. Total recursion! Development started in 1990 (before Linux kernel) as part of plans to create fully free and open source operation system. Unlike the Linux kernel Hurd have a lot of system daemons (you can see it on video) run by GNU Mach microkernel and some specific system protocols. Popularity of Linux lowered Hurd’s priority, but project progress all this 25+ years.