http://www.ethernut.de/en/software/index.html Nut/OS is an intentionally simple RTOS for the ATmega128, which provides a minimum of services to run Nut/Net, the TCP/IP stack. It's features include: + Non preemptive multithreading. + Events. + Periodic and one-shot timers. + Dynamic heap memory allocation. + Interrupt driven streaming I/O. Main features of the TCP/IP stack are: + Base protocols ARP, IP, ICMP, UDP and TCP. + User protocols DHCP, DNS and HTTP. + Socket API. + Host, net and default routing. + Interrupt driven Ethernet driver.