The interface is physical
I build custom mechanical keyboards because they make interaction design impossible to reduce to pixels. Switch weight, spring return, plate material, key profile, firmware, case resonance, and desk acoustics all change how a keyboard feels over a long session.
One build was designed to evoke the look, sound, and deliberate action of a typewriter. The interesting part was not styling it like an old machine; it was tuning modern components until the feedback carried some of the same character.
The workbench is iterative: solder, assemble, listen, type, disassemble, damp, remap, repeat. Small physical changes can have a disproportionate effect on comfort and flow.