In the past...
I've been in the habit of using my PC hand-me-down hardware for my pet projects at home. But recently reconsidered trying out an Intel atom based SoC server board. Unfortunately as Intel seems wont to do these days they are bit miserly with PCI-e lanes. If only something like this IBM kit were available reasonably cheap. Not for a supercomputer mind you. 24 threads is totally not overkill for testing out software.