OSDev.org

Has there ever been an OpenRISC chip produced?

This is actually something I've been interested in developing for years. Well, not specifically for OSdev, but just in general.

I'm a big fan of SPARC, and SPARC seems to be the most open friendly ISA, so I'd be using LEON, a completely open source VHDL implementation of SPARC32 v8

For graphics, I agree that it is best to generalize do it in software instead. There is an open so-called GPGPU on github which looks very promising. There's also an open source Cray-1 implementation (although this is nowhere near fast enough).

Getting an FPGA big enough to fit all of this would be quite a task though.

If you'd rather develop for x86 (since there tends to be better resources for doing so), the "86Duino" board might be good platform to target. It's based on a Vortex86EX SoC, which is well-documented. The supplied firmware is based on FreeDOS (but it'll boot any OS from a mini-SD card) and full source to the Ardino-like runtime environment is available and relatively easy to follow (so getting things like GPIO to work from a custom OS should be pretty simple).

The only downsides are the lack of built-in video output (although mini-PCIe video cards do exist and would work, alternatively, an Arduino-compatible LCD module could be used) and the relatively low specifications (300Mhz i686, 128MB RAM).

There's also the Intel Galileo board, which is similar (400Mhz i586, 256MB RAM), but is a bit more expensive and seems to have a somewhat more complex architecture.