By far most of my side projects died before seeing the light of day. Either because I lost interest or I found another project that did what I aimed to do better than I imagined.

Only a couple went live but didn't get traction: - A site for ip geolocation lookup - A curated index of conference talks and meetups

Last year I decided that I'd do much more market research before writing any code, and that I'd see it through all the way. So I'm working on https://www.nslookup.io for about half a year now, which isn't profitable yet (€50 monthly cost). I'm still confident I can get it profitable. There's enough search traffic, other tools have horrible UX, and I've committed to spending time on it at least weekly next year.