The Contiki OS Version 3.0 Released
contiki-os.blogspot.com
contiki-os.blogspot.com
https://github.com/contiki-os/contiki/tree/3.0/platform/c64
https://github.com/contiki-os/contiki/tree/3.0/platform/c128
Great OS to experiment with, but I would not recommend building a business on top of Contiki today.
If you're looking for a lightweight OS that does low-power IP networking with built-in support for self-healing wireless meshing, I think it is difficult to find an OS that beats Contiki. Take this from someone who has in fact built a business on top of Contiki :)
It was a case of "poorly implemented and poorly tested". I know lwIP is widely used, so I'm sure it's not all this bad. However, that was still a pretty big red flag for me.
Not sure about Coffee in particular though, simply because file systems isn't really the focus of Contiki. Unlike server and desktop OSes, where the file system really is a core item, embedded OSes like Contiki don't depend on them and they are only used by a small subset of applications.
I think it is a great open source RTOS. FreeRTOS and Contiki are good but not really comparable. Their focus is on smaller more memory constrained systems.