Useful keyboard resources
Gui program for on the fly remapping keymaps
Vial - https://get.vial.today/
Gui program for on the fly remapping keymaps. In my opinion, slightly more powerful than VIA
QMK Firmware - https://qmk.fm/
Links to the github repo, official documentation also on github, and QMK Configurator
M3tt3o's How to build a custom keyboard book - https://matt3o.com/book/
Just a wonderful source of information on keyboards, everything from the basics, down to handwiring a keyboard and building your own QMK firmware.