I'm working aggressively to diversify my income and reduce my expenses myself. The best source of income is that which requires nothing from you to produce. So along those lines...

Running a company requires great effort. Putting others in charge and incentivizing them (profit-sharing, equity stake, etc) requires little effort and becomes passive income albeit reduced... but now I'm free to rinse and repeat.

Flipping real estate takes effort. Renting real estate takes little (assuming you have a third party handle the management)

Actively trading in markets requires effort. Passive income on capital deposits (used to) require no effort.

Because of fiscal policy even precious metals are effectively passive income producing from the perspective of a fiat currency world, though thats not strictly true.

I apply this principle universally...
Growing corn for food requires great effort. Planting sweet potatoes requires virtually none.