I discovered the Castle Airdrop Project a few months ago and found it very interesting. Their platform allows other projects to use them to distribute their coins via airdrop. If you hold CSTL in your wallet you are eligible to receive airdropped coins.
This model is different than the "spam your twitter followers and post your Eth address" or the "You get X coin for every BTC you hold". It is dependent on the coins you hold but the cost of entry is LOW when compared to needing to hold BTC or Eth.
For me at least the bonus is that I don't have to spam social media to qualify for the airdrops.
Twitter:
https://twitter.com/Castle_CSTL Discord:
https://discord.gg/sfaU8EyWeb:
https://projectcastle.tech/