The stock market. Not something I really envisioned myself investing in. But with apps, it has gotten a lot easier for people to invest themselves with little money. You can put in just a little bit and make a small profit. But some of these apps, like Robinhood, also give you a free stock just for signing up. So even if you don't invest, that's free money right there.
Most likely you'll get a stock valued at $10 or less (still free money) but you do have a chance of getting one worth much more than that. And guess what?! . . . I did! My free stock was for Visa, which at the time I received it was worth over $200. I decided to keep it in to see if it would raise (it has since gone down) but that is still money that I can get at any time more than I had before.
So try it out yourself and see what you get!