Some people play sports or do the crossword. I like to rebuild sites with a angle on playing with media and content experiences.
My one recurring project is Article Rocks, a simple aggregator that I redo every so often. At one point is was a small web app that pulled in AMP versions of articles, later I added a offline component, and then a couple of years back I gave it its own domain and switched it to the horizontal digestible content format.
It can best be described as multiple aggregation points + image filters + basic sentiment analysis + interruptors (curated gifs, simple ads, messaging) with a focus on mobile (not optimized at all for Desktop). It updates every 15 minutes and refreshes sources. As time permits I rebuild, break, optimize, or extend it.
It allows me to challenge my own assumptions on how things should work - and also dig into into issues of load time and perceived user load time. (It has an decent PageSpeed score hitting 100 at one point).
Its a lot of fun. It keeps my skills current, and I actually rely on it for my subway commute. Win-win.