Lots of things over the last decade or two. I can count almost one hundred repos on GitHub, but most of them are not very popular with other people, my projects seem to only scratch my own itches..
I have my own lunisolar calendar and decimal time (with centidays and dimidays) so I produced a lot of code for that on various devices. I also wrote two chess engines and a hobby operating system.
And countless web apps, like one to read the daily/monthly top of HN and Reddit, another to host my pictures (on a cool domain hack), one to manage the batch jobs on my chess engine cluster in a rack at home that helps keeping the house warm in winter, and lately my own frontend to Bing API because I was growing dissatisfied with DuckDuckGo.