Without investment it is impossible to earn ETH, it is possible to earn ETH through bounties. Bounties are the best way to earn some token my promoting their campaign and we can easily convert them to ETH.
Some bounty, where the companies promoting the project are paid not on the token platform and in Ethereum. But projects that pay in Ethereum are very few and they appear rarely. I try to sell 50% of the tokens I earned during the bounty of the company and exchange them for Ethereum, so I get a free Ethereum