ultrasquid

I’m not sure if its open source, so technically not FOSS, but Connect is by far my favorite UI and UX wise.

Turn it off, REMOVE THE BATTERY (important step, batteries are dangerous and do not like liquids), then disassemble it. Remove the keycaps and rubber membrane and wash them with soapy water, and wipe down the gold contacts with isopropyl alchahol. Wait for it to dry completely before reassembling it.