[coreboot] What are the best motherboards/systems out there for open-source software?

[David Christensen]

coreboot:

I am researching parts to build a new open-source desktop system, and came
across coreboot tonight.

I have heard of open-source projects to implement x86 BIOS, but have always
wondered how they fared given the fact that most motherboard vendors and chip
vendors consider their products confidential intellectual property and won't
provide technical documentation necessary for software development without an
contract (NDA, etc.).

Are there any modern x86 motherboards and/or systems currently available for
which technical documents are available for the motherboard and everything on
it?

Are matters better or worse for alternate architectures?

David