Firmworks has a open source implementation of OpenFirmware which is part of the OpenBIOS project, can be used with Coreboot, and implements TCP/IP with various protocols including HTTP, all in Forth.
Interesting. Looks like there aren't many drivers, though. I only see stuff about running it through QEMU or Virtualbox.
Maybe somebody can try running it from OpenFirmware (see my my sibling post to yours), which has been ported to lots of platforms, and has lots of code one could borrow from in the way of drivers. Of course at the end of the day I guess the point of QEMU / Xen is to use Linux as a device driver.
http://www.firmworks.com/ofwfeatures.htm
http://GitHub.com/openbios/openfirmware