Aside from typical bounty campaign and airdrop. Now the hype change to incentivized testnets. ..
Completing tasks in the test network sometimes brings a good profit. One of the last such examples was the airdrop from Aptos, in which for mint free NFT in the test network, its participants received 150 APT, which is approximately equal to $1200. By the way, the activity in this test network has not ended yet, since only 3% of the 51% allocated to the community has been spent.
The main problem of many projects is that you may not receive a reward. I tested zkSync a long time ago, yesterday I spent $40 on various bridges and exchanges, and it's not a guarantee that it will give me a guaranteed airdrop.It is better to apply to the ambassadors, then there are more chances to get project tokens.