One can also chord on conventional keyboards. A cheap keyboard with 2KRO (2-key rollover) and 4 modifiers, might be held upside-down, providing Shift/Ctrl/Alt/Meta plus a key or two. And a 2KRO with 8 modifiers (left and right aren't merged) might be used two handed. Some keyboards special-case common key sets like WASD. A 6KRO keyboard permits one-handed chording with arbitrary keys. USB boot-mode keyboards are limited to 6KRO plus 8 modifiers. :/ Full n-key rollover (NKRO) USB HID keyboards exist, but last I looked some years ago, it was a niche mess.

A half-century on, an we still can't play keyboards like pianos... "if your customers aren't complaining loudly of being crippled, you're overbuilding".