Down For Everyone Or Just Me
https://downforeveryoneorjustme.com/
Makes ~$1,000 a month gross, lot less after AWS costs.
I've had it for a long time, but haven't done much with it because of my primary business. After I sold that I spent the last year playing with some ideas and testing. I am working to get a new design up and just partnered with a friend to redo the arch and let him see what ideas he has to better monetize it.