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The Hurd unikernel project is based upon 'rump kernel' technology. I'm not up to date with this status in Hurd.
http://darnassus.sceen.net/~hurd-web/rump_kernel/
https://archive.fosdem.org/2016/schedule/event/microkernels_hurd_rump_sound_usb/attachments/slides/951/export/events/attachments/microkernels_hurd_rump_sound_usb/slides/951/2016_01_30_fosdem.pdf
The L4/Hurd project is inactive. At the moment, all the community effort is with GNU Mach.
https://www.gnu.org/software/hurd/faq/which_microkernel.html
Personally, I've had a dream to start a Hurd VM and hack around with some hardware drivers within Hurd. It's taken me 12 months to go through my Linux driver education project so now I've got a foundation for this to happen.