seL4 / seL4

The seL4 microkernel

RT-Thread / rt-thread

RT-Thread is an open source IoT Real-Time Operating System (RTOS). https://rt-thread.github.io/rt-thread/

HelenOS / helenos

A portable microkernel-based multiserver operating system written from scratch.

Supercip971 / WingOS

a little 64bit microkernel based operating system written in c++ with smp support