A Unix-like operating system based on the GNU Mach microkernel from Carnegie Mellon (Hurd and Mach make up the GNU Hurd operating system from the GNU Project). Hurd is known as a "multiserver" operating system, which enables system components such as file systems to be added by the user that otherwise would have to be incorporated by the operating system developer.
Quite the Name
Hurd stands for "Hird of Unix-Replacing Daemons," and H-I-R-D means "Hurd of Interfaces Representing Depth." Go figure. But better yet, tell your colleagues you want to use the "Hurd of Interfaces Representing Depth of Unix-Replacing Daemons," and see if they invite you to lunch again! See GNU Project