I run a language learning site / web app that is totally free, no ads too, going on about 8 years now. It's for one specific language that has not had much attention from the software community but could use it.

I've never tried to promote it and have never updated it much, but there have been some random people over the years who have given me money. I had a few people send me 50$ unprompted, plus some people I met IRL pay for dinners and things like that when the topic came up.