I spent a couple years building https://infiniquest.org in my spare time. This is a site where you can both create and play interactive fiction games, using an engine I built entirely from scratch. I mainly built it to prove to myself I could complete a large project start to finish. I also had the motivation that my son and I could make games for each other, but by the time I finished, he was big into Minecraft and had no interest in text adventure games. :D I had hoped to make some income with it thru ads and paid features, but I never tried too hard to build up a user base, and now it sits there largely unmaintained for the last several years. Last year I completed a proof-of-concept integrating it with the Amazon Echo - that was kinda neat, but there's a lot of work to be done to finish and polish it... and considering there were no users to begin with, I lacked the motivation to undertake that.