It turns out that a "cluster" (even of two; and I rather like the term "circumference" for 2 RPis!) is actually what I want to do. I want to learn how parallel computing works (clearly I have a long way to go) and be able to write code that I can actually test.

Ah well.. Thank you for replying! And I'm checking out the Bramble now.

Is it possible to use two Raspberry Pi computers together in such a way that the result is effectively one dual-core computer? If so, how would one go about implementing this? My apologies if I don't use proper terminology, if I'm being unclear, if there's already a thread regarding this (I couldn't...