I would like to also add gambling. There are gambling sites before that gives small amount for you to gamble. Idk if it's still available until now from that site where I've seen it but I'm pretty sure there are a lot of gambling sites which gives free coin to be gambled that I don't know since I don't use to gamble with many sites.
most of the gambling sites would only give a bonus after you met the requirements like you must deposit an (xxx) amount before you received your bonus in the gambling site you have choosen to gamble. Gambling sites is not the most suitable idea in how to earn cryptocurrency for free. Another way to earn cryptocurrency is to start a service program which you work for them in exchange for cryptocurrency. If you're a developer then you can earn cryptocurrency when a group of people hired you as their developer for their site. This is the as earning cryptocurrency for free without costing any amount of money.