The art of creating very tiny programs for the 80x86 family of CPUs
Smallest program I ever sold, for near-5-digit profit, was a "REBOOT.COM" which saved a sysadmin from hand-rebooting 200 machines, daily, and which earned me $9,000 on account that it was my monthly rate at the time, and its all I did that month, by circumstance, anyway ... it was a different time, and I honestly felt I deserved it, then[1].C:\> debug.com
n
JMP FFF0
w reboot.com
q
^Z(or at least, it was something like that...)[1]- Now, not so much.