Sorry, I haven't had the time to look into these. I don't know they're worth anything, but so long as you don't have to send them any cryptos, I don't see the harm in trying. I certainly wouldn't give them any real personal information, just in case they're scams.
The first 2 are given to for just holding ETH or NEO, the 3rd you have to sign up. I probably won't be doing that one.
Time is very short, but so long as you have some cryptos in your own wallet, you'll be able to claim the corresponding airdrop.
Xenon (ETH)
https://ledgergazette.com/2018/02/11/xenon-xnn-price-down-23-2-this-week.html
Ontology (NEO)
https://cryptocrimson.com/neo-holders-to-get-ont-ontology-tokens-airdropped/