Contiki is an open source, highly portable, multi-tasking operating
system for memory-constrained networked embedded systems written by
Adam Dunkels at the Networked Embedded Systems group at the Swedish
Institute of Computer Science.

Contiki is designed for embedded systems with small amounts of
memory. A typical Contiki configuration is 2 kilobytes of RAM and 40
kilobytes of ROM. Contiki consists of an event-driven kernel on top of
which application programs are dynamically loaded and unloaded at
runtime. Contiki processes use light-weight protothreads that provide
a linear, thread-like programming style on top of the event-driven
kernel. Contiki also supports per-process optional preemptive
multi-threading, interprocess communication using message passing
through events, as well as an optional GUI subsystem with either
direct graphic support for locally connected terminals or networked
virtual display with VNC or over Telnet.

Contiki contains two communication stacks: uIP and Rime. uIP is a
small RFC-compliant TCP/IP stack that makes it possible for Contiki to
communicate over the Internet. Rime is a lightweight communication
stack designed for low-power radios. Rime provides a wide range of
communication primitives, from best-effort local area broadcast, to
reliable multi-hop bulk data flooding.

Contiki runs on a variety of platform ranging from embedded
microcontrollers such as the MSP430 and the AVR to old
homecomputers. Code footprint is on the order of kilobytes and memory
usage can be configured to be as low as tens of bytes.

Contiki is written in the C programming language and is freely
available as open source under a BSD-style license. More information
about Contiki can be found at the Contiki home page:
http://www.sics.se/contiki/