There was the idea for solar-powered slotcar freeways, and the idea for something else, I forget what. Here is another idea for the world that I have been carrying around since I was a kid. I can’t figure out how to get rich from it, though, so I’m putting it up for grabs here:

Reciprocal development aid. By this, I mean not only would rich countries send aid workers to poor countries to drill wells, or vaccinate, or work on industrial development programs. Poor countries would also send teachers to rich countries to train people how to undevelop, and live with less.