Homebuilding would be active income, since you can only sell each house once. Game development would be a good example for someone like the Minecraft creator. He invested a bunch of time creating this cool game, and then he sat back and got rich. It’s passive at that point (assuming no maintenance, bug fixes, etc.), since he continues to gain sales, despite only doing the work once. The digital realm is full of opportunities for passive income, or at least it used to be. Corporations have essentially shoved individual creators out of the market.

Edit: I’m aware that the Minecraft creator sold the game, but was using his earlier experiences as an example. I read an interview with him once and he said “I think I was already rich by the time I thought ‘holy shit, I’m going to be rich!’”.