It's an operating system for little computers :-)
Got all the main things you'd like in a modern OS (gui, TCP/IP stack, co-op multitasking .. maybe preemptive as well) just crammed into 64k or less ... the C128 port needs to be brought up to date (to version 2) which probably isn;t a simple task, but the source is mainly in C (cc65) with machine specific bits in assembler.