Microkernels and hypervisors are very closely related in the view of some. Paravirtualization, like L4 Linux, is when the guest is aware of being hosted and, at one time - maybe still, could outperform guest OSes on fully virtualized hardware. I'm not sure if that's all still true since Intel and AMD implemented VTX.

If you want to see a neat demo of this stuff - check out the DROPs demo or TUD:OS http://demo.tudos.org/.

Screenshots of a whole bunch of linuxes (linii?) running at once: http://demo.tudos.org/l4lx_screenshot.png

I think this is from 2003...