The GNU Hurd is an operating system based on a microkernel design with seperate userspace processes in seperate address spaces. Linux uses a monolithic design, with many operating system components running in kernel mode with full privledges. With the microkernel design comes several advantages.
Traditional code in the kernel includes the filesystem, TCP/IP stack, device drivers, etc. Many of those components are in userspace on the Hurd. These components can be written in languages other than C or rust, like perl, lisp, haskel, etc.!
While we believe that the Hurd is one of the better microkernel operating systems, there are a few others that exist: Genode, Redox OS, Helen OS, and others.