Not mechanical, but little semi-modular analog drone synths are in a similar wheelhouse. Because every knob has a dedicated function and, other than a few default routings, you’re directly patching the outputs to inputs themselves, it gets that feeling of visible connections and settings that you have tactile control over. Plus, because the emphasis is on textures/soundscapes, you don’t need formal music training to get good results.

Neutral Labs makes one, stylophone has one coming out in the near future, there’s a ton of boutique one-offs on Etsy. EDIT: have to add the Bastl Kastles, very portable and easy to learn.

There are some truly mechanical musical tone devices out there, but they tend to either be too large to be portable or are very limited.