ClockworkPi
ClockworkPi makes some interesting devices.

I've owned the following:
The full Linux machines support a CM\(n\) module; Clockwork has also released their own CPU boards. The two ARM boards are the A04 and A06, and there's a RISC-V board (the R-01).
Links
- Forums
- Community downloads (for all A06/CM\(n\) devices)