This is a cheaper alternative for adding a HEX-keypad to the RC-ONE computer (KIM-1 replica), it's not comfortable to use in the long run though you'll have access to all of the functions expected from the classic computer designed by the late Chuck Peddle. MOS was famously bought up by a somewhat unknown typewriter-manufacturer named Commodore, so the computer was also later rebranded as the Commodore KIM-1 and shares the key-layout I've used!

Also see my other shared projects for a more comfortable version of the keypad, the Keypad MX. The MX-edition uses Cherry MX compatible keyboard switches instead of the momentary tactile switches, but due to the added cost of the components I created the SX-edition so that a complete RC-ONE can be put together without spending too much on it. Either way, everything is modular so you can later choose to upgrade if you should desire to do so. Also of note, the MX-edition also has a companion-module for adding an Arduino Pro Micro to it so that it can be used on your modern PC as an actual HEX-keypad.