This is a keyboard firmware based on the tmk_keyboard firmware with some useful features for Atmel AVR and ARM controllers, and more specifically, the OLKB product line, the ErgoDox EZ keyboard, and the Clueboard product line.
The docs are hosted on Gitbook and GitHub (they are synced). You can request changes by making a fork and pull request, or by clicking the "suggest an edit" link on any page of the docs.
The project also includes community support for lots of other keyboards.
QMK is developed and maintained by Jack Humbert of OLKB with contributions from the community, and of course, Hasu. The OLKB product firmwares are maintained by Jack Humbert, the Ergodox EZ by Erez Zukerman, the Clueboard by Zach White, and the Atreus by Phil Hagelberg.
http://qmk.fm is the official website of QMK, where you can find links to this page, the documentation, and the keyboards supported by QMK.