Hláškovník
This is probably my longest running project. It started sometime around 2015 and I am maintaining a version of it until today. It was my first web project with a proper backend and database and while developing it, I learned so much about the web and, because my friends kept attacking it incessantly, I learned about things like SQL injection, spam protection and other important ways of keeping a website (more or less) safe. A few years back I rewrote the entire thing and this new version is on GitHub. The old version is private, because it stinks, but I might end up publishing it at some point.