Key Tester

Switch Hitter - elitekeyboards.com

Keyboard Diagnostic Software

https://web.archive.org/web/20190428204254/elitekeyboards.com/switchhitter.php

Aqua'S Key Test

https://geekhack.org/index.php?topic=34670.0

Keyboard Tester

https://github.com/jnewing/KeyboardTester

xev

xev -event keyboard -event button

showkey

showkey -s