There were FOSS Tongue-driven and Air-switch (Puff/Blow Morse codes) wheelchair control interfaces with generic USB HID mouse/keyboard emulation. They also have normal pointer interface modes with desktop and tablet OS (no janky software required.)

The projects were necessitated because costs of medical-device regulatory barriers made hardware iterations economically infeasible to mass-manufacture. There were a few university faculties that would show up at community events to demonstrate DIY kits folks could put together with a friend.

If these projects are no longer available, send up a flag and someone will spend a few weekends to bring up more open-hardware options. One can't legally sell these as a medical-device in most places, but there is likely nothing stopping a low-power hobby "game control" kit. =3