Re: Contiki, there was an x86 port, but the current version doesn't list it as a supported architecture in the current tree. If you can speak German there's a lead on it here:

http://hitmen.c02.at/html/tools_contiki.html

Note that the focus of the Contiki project has changed *a lot* since the days when people were all excited about using it to get their Commodore 64s or Apple IIs "online". Essentially all the work now is concentrated on using the Contiki kernel as a real-time embedded OS on microcontrollers, with essentially no mention of the cute semi-windowing UI the 1.x tree started with. As a "personal computer" OS at this point it's probably something of a dead end.