A famous example of this is the “lego batch scheduler” that is the stuff of hacker legend, but I’m struggling to find a writeup about it online.

The story goes some company/university/whatever in the early days of computing wanted a batch scheduler[1] to run jobs at specific times on their big IBM mainframe. They spoke to IBM who quoted them an eye-watering amount for it and said it would take months to implement. The main system operator told them to just hold fire and he’d see what he could come up with. The next day they had a working batch scheduler for zero dollars. He had set up the jobs so they would run on a keypress on a particular keyboard, then taken some of his kids’ lego and made a long finger on a hinge. He wrapped some string around the winder of a wind-up alarm clock then attached it to the lego and set the alarm clock to go off at the time they wanted to run the job. This had the effect of unwinding the string, lowering the finger that then pressed the key on the keyboard, running the job.

Not only that, but the jobs had a problem if you tried to run them twice, so he made it so the lego brick snapped off when pressing the key, making the job idempotent.

[1] Think “cron”, but for a mainframe