Standalone keyboards firmwares
There is a presentation that list various free software firmwares for keyboards.
Laptops keyboards firmwares
Several ARM laptops also have a free software firmware for the embedded controller and/or keyboard controller.
TODO: list the laptops, if they can boot with only free software and the firmware of the embedded controller and/or keyboard controller.
Laptops keyboards without firmwares
Sometimes the keyboards keys can be connected directly to the System on a chip and Linux drivers like gpio-matrix-keypad can make the keys act as a keyboard.
Standalone keyboards without firmwares
TODO: research the topic.