numlockx
A program with exactly one job: switch NumLock on when X starts, so the keypad produces digits from the first keystroke.
The BIOS could turn NumLock on at boot, but the X server paid no attention and started with the light off. Anyone typing a password on the keypad got arrow keys instead. Luboš Luňák, better known for his work on KDE and KWin, wrote numlockx around 2000 to fix exactly that: numlockx on, off or toggle, using XKB where available and a faked keypress through XTEST where not.
The line ended up in .xinitrc, in XDM's Xsetup for the login screen, and eventually as a checkbox in desktop environment settings. That such a program was needed at all says something about how many corners X left for its users to sweep themselves.