This watch is actually capable of running custom software and there was a single cartridge of software available for it at launch. No other software was ever made for it until 2017 when a developer reverse engineered the whole thing:

https://github.com/azya52/seiko

https://www.hackster.io/news/reverse-engineering-the-world-s...

Everything about the watch had to be figured out from scratch from the communications protocol to the CPU instructions. It's pretty cool to see a device from 1984 actually getting some "new life" in this way.