Markus Redeker π@Scmbradley You could also try fludics (https://en.wikipedia.org/wiki/Fluidics), the use of gas or fluid stream to perform logical operations.
There was even a simple fluidic computer, the FLODAC (https://gwern.net/doc/cs/computable/1964-gluskin.pdf). It was only meant as a proof of concept and had a memory of four 4-bit words. But it worked and could do at least one nontrivial computation.
But nowadays, with 3d-printing, it could be possible to build a larger and more powerful version of the FLODAC β a kind of ultimate retrocomputing project.
