I run https://www.weheartswift.com/ the first site dedicated to the Swift Programming language.

I've wrote a book that teaches people how to code in swift from the ground up. https://www.weheartswift.com/swift-programming-scratch-100-e...

I've also made an exercise platform similar to codeschool/codecademy/etc that is available as a mac app using playgrounds or online by using our swift sandbox https://www.weheartswift.com/swift-sandbox/

The site generates about 30k/year in revenue growing at a steady pace. Operating costs are around 10k / year for servers/software/subscriptions/marketing.

I need to spend about 2 weeks yearly updating the book/app to the last version of swift. I also spend about 5 minutes per day replying to customer emails. It's not that passive, but really close. (ignoring time spent developing products/book)