Comment by comex

"Nothing over the main Linux kernel" is complicated. It offers a microkernel design that was modern and radical 20 or so years ago, and is still pretty unique as a Unix system; Linux being as monolithic as ever, you can still do some pretty cool stuff with it you can't come close to with Linux. However, afaik, these days the designs of Mach and Hurd aren't looked upon very highly, the stability advantages of microkernels aren't as important anymore with rock solid traditional kernels, and instead of figuring out how to empower non-root users on Unix systems we just give everyone their own VM.