proof of stake was first proposed in 2011 on bitcointalk, the go-to reference for everything bitcoin/altcoin.

https://en.bitcoin.it/wiki/Proof_of_Stake

http://wiki.nxtcrypto.org/

http://bitshares.org/security/delegated-proof-of-stake.php

If any coins make it you can see at watching the marketcap of the coins at http://coinmarketcap.com