Contiki at

13 December, 2007 - 16:58 has a three-part
article series on "Choosing the best system software architecture for
your wireless smart sensor design" that covers SICS' Contiki operating system:

"The benefit of being able to change the application code while preserving the relatively static RTOS kernel is attractive, especially when precious energy needs to be spared while transmitting only the bytes
of the changed application or part of the application to the device. A
good example in this area is the Contiki RTOS. The curious reader is
advised to take a look at [6], which is an excellent paper."

Part one of the article and part two of the article.