It occurred to me today that it might be useful to make a list of all the ways to earn money through either actual programming or just programming knowledge. I imagine it's probably a finite list as long as you stick to a reasonable level of granularity. Here's what I have so far:

• Trading your time for money (i.e. having a job or being a freelancer)
• Building your own software product (a full-fledged startup or a tiny mobile app or whatever)
• Giving talks at conferences and meetups
• Teaching students in a classroom
• Writing a book or blog (these are products, but non-software products)

I've probably missed at least a few. What else is there?

(I'm not sure whether this is an appropriate question, by the way. I think I would select the best answer based on how practical/original/interesting/numerous your suggestions are.)