Not completely passive and not really a side project, but my wife's business is teaching Latin (the language; I mean not the programming language, the language

Not completely passive and not really a side project, but my wife's business is teaching Latin (the language; I mean not the programming language, the language people actually speak; well, some people speak) on the Internet. She has an evergreen funnel which actually converts a few sells per month. I do the programming, hosting and server maintenance for that thing. She creates the actual content. Of course this is not completely passive: she periodically publishes free material to keep attracting people to the funnel. But it's quite rewarding every now and then to have an email saying that some random guy bought the videocourse. The name is Satura Lanx: https://www.youtube.com/channel/UCJCYCaXUERhY93xEWC8Cojw https://www.youtube.com/channel/UCJCYCaXUERhY93xEWC8Cojw