20 years ago I met a young woman in her mid 20's. She's setup coloring book pages with google ads by the thousands, in pretty much every language. Her income from that was around $8K a month, and this was late 90's?
Similar story, but for the mobile era: I knew an indie app developer who built a portfolio of early mobile apps. His top-earners were a coloring book app, bead animal patterns, and a no-essay college scholarship app. Those three allowed him to pay himself and a partner salary and drop contract/client work.
