Pi is a new digital currency being developed by a group of Stanford PhDs. For now, you can join the invite-only beta to earn Pi and help grow the network. Your phone does all of the work for you. People who join during the beta phase can become contributors and mine at the highest rate and gain special privileges. During beta, coins are distributed at a fixed rate and then once out of beta, will be officially mined. Either way you get to keep the coins for free!
Go to https://minepi.com/
Download the App...
Because it is invite-only, the app is going to ask you for your referrer, type "iguessitsokay"
Enjoy mining on your phone...