Horizon is a research project aimed at developing a 32-bit Operating System for the Intel architecture. It's written in C and assembler (GAS syntax) and one of its main characteristics is full network integration.
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.