Ask HN: Side projects that are making money, but you'd not talk about them?

One night in 2013 I had this stupid idea that people would start searching google for "who is retargeting me" just like they do with "what's my ip" — I've created in 30 minutes, bought the domain whoisretargeting.me and put Google Ads. It's made €7000 in 7 years. (1) Do you have projects like this?

(1) https://pasteboard.co/JbPKJRs.png