Unconventional computing is computing by a wide range of new or unusual methods [including] … optical computing, quantum computing, chemical computing, natural computing, biologically-inspired computing, wetware computing, DNA computing, molecular computing, amorphous computing, nanocomputing, reversible computing, ternary computing, fluidics, analogue computing, human and domino computation.

I’d still like a mechanical computer, I guess they have been testing some new designs out: https://www.tomshardware.com/pc-components/cpus/kirigami-mechanical-computer-has-high-density-memory-and-doesnt-need-electricity-researchers-demo-new-mechanical-computing-design

Domino and billiard ball computers sound like interesting “just for fun” designs:

https://infogalactic.com/info/Billiard_ball_computer

https://infogalactic.com/info/Domino_computer