Yes, there are still a lot of airdrop that have no requirements an existing ETH in your wallet
when you join it, so if in your wallet there is no balance, you can follow the airdrop, in fact there are some airdrop that has the requirements in our wallet must have some ETH, or we must send some ETH
to the developer's, the purpose is to speed up and facilitate them in sending coins or tokens to our wallets, because every transaction in etherdelta we must have some eth for gas, but nowadays there are so many scams under the pretext of airdrop, they require us to send some eth to the wallet them but we do not get coin or tokens from them.
After sending coins to them usually a lot of regret because the coins that have been transferred can not go back
Instead of doubling coins it's just a hoax of people who are not responsible for reaping profits.and actually it's a scams.