A lot of custom-built or ethusiast-level keyboards such as the Planck, Zeal60, Let's Split and many more use an open-source firmware called QMK. This firmware allows you to freely define your keyboard layout and add a lot of functionality (i.e. emitting a different keycode on long and short keypress, dual-function keys, leader keys (think of vi's :)). We could use the Hack Week to add functionality, check the source code for security issues and add support for more keyboards.
Check and extended the QMK Firmware for mechanical keyboards
