LUnix (little UNIX) is an operating system for the Commodore64 - a famous home computer back in the 80s. It supports TCP/IP networking (SLIP or PPP using a RS232 interface). LUnix aims to look and feel like UNIX.
Liquorice is a multithreaded SASOS for use in embedded systems (8 bit and up). Includes a small but working IP/ARP/ICMP/UDP/TCP stack with SLIP, PPP and Ethernet support.