The airdrops was first do by blockchain you can read my old post about it . The airdrops is 2 to 3 years old program in this program the airdroper will give you some of task to do. You need to done it. Task like follow on tweeter or medium and like on facebook. And Youtube subscribe .and after doing this tasks the airdroper send you the tokens or some of coins as a your payment after recive you can exchange the coin or tokens with the btc and ether and earn you can earn 100's of doller from here try it