A long time ago I created a free website/service to play with scenarios and forecasts for variable-rate mortgages - it was specifically for the Italian and Span

A long time ago I created a free website/service to play with scenarios and forecasts for variable-rate mortgages - it was specifically for the Italian and Spanish markets (where those kinds of mortgages are very common). Monetization was only adsense and one affiliation program. I made around $100/month for at least 3 years, with almost 0 maintenance and just some SEO work - until the server broke down, and I was too busy with other projects to set it up again. Don't know if the same approach would work today with falling ads revenue, but having something that is completely free to use has the advantage that there is no customer support and no stress.