Airdrop is a way for a blockchain project to distribute free tokens/coins in order to introduce to the crypto community their developing project, based on the assumption that the wider the user base, the higher the value of a coin. The purpose is to gain an early community of users for a particular token, coin or project.

The following list contains a list of active aidrops:

cryptrivia
skraps
FAN Token
TrakInvest
Stox - Sign up to receive tokens
Orca Alliance
VuzzBee - Sign up to receive tokens
Bethereum - Join bounty to receive tokens
Apollo DAE - Chat with the bot on Telegram and submit your details - Website
Invacio - Sign up to receive tokens
Synthetics - Sign up to receive 100 SYNT tokens
ALTS Token
Suchapp
Aelf
NKOR - Sign up and complete simple tasks
BitcoinToken
CrowdCoinage
Obirium Sign up to receive 50 OBR tokens

Although the value of these airdrops is relatively small, we have to consider that they are giving it for free and we do like free coins! Who doesn't? :) Morower some of them might gain higher value as well over time. Who knows?

I will try to expand the list while keeping it updated as much as possible and do hope that you'll enjoy the "coin hunt".

Every airdrop has a different set of rules, please DYOR before signing up an any project.
Most of the airdrops require actions to be completed on Telegram, Twitter or other social media accounts to be eligible for free crypto tokens.
You certainly will need a wallet address on which you can receive the tokens, ex: MyEtherWallet
Do not use an exchange wallet address from Coinbase, Bittrex, Binance, or any other. You need a personal address where you control the private keys! Never give your private key or other sensitive information to any of these websites!