[naasking]

The first PowerPC linux for the Power Mac ran under the Mach microkernel [1].

Then there was also L4Linux, which I believe was the first low-overhead virtualization of Linux using the L4 microkernel. Papers demonstrated < 10% overhead I believe, where previous virtualization efforts were somewhat higher. I'd say it kicked off the whole paravirtualization/virtualization craze.

[1] http://www.mklinux.org/