I heard a game described, a variant on tic-tac-toe, that I couldn't figure out how to completely dominate, so I figured I'd make it so I could see if it's as fun as described, and not trivially simple.
I saw an abandoned project idea, thought I could make it interesting, and, I think, largely succeeded.
I made a chat room that works like normal rooms: you only really hear the last thing someone said. Everything else is your own personal memory.
A web version of a card game I learned in college.
A timer and stopwatch. Totally unimpressive in every way, but free of ads.