On this day, in 1991, Linus Torvalds first announced Linux to the world, in the comp.os.minix Usenet group. I had written a tiny bit of code in that code: the string formatting parts of the kernel logging function printk.
Today, that code (with changes and improvements by other people) runs on billions of devices, on all continents, on all oceans, in orbit, and on Mars. Possibly other places.