Don't forget the original (for Linux anyway), SEL4.
https://sel4.systems
Also, seL4 comes from a long line of L4 microkernels (https://en.wikipedia.org/wiki/L4_microkernel_family#History) which actually predates Linux (L3 was developed back in '88).
Don't forget the original (for Linux anyway), SEL4.
https://sel4.systems