Casper is a security-deposit based economic consensus protocol that is set to eventually replace the proof-of-work incentive system currently in place for the Ethereum public network. The developers working on CASPER include Vitalik Buterin, Greg Meredith, and Vlad Zamfir.
My recommendation is to read these links in order to gain the best perspective on the thought behind CASPER proof-of-stake previously vs today:
Latest CASPER Specification/Implementations
Community Discussions of Interest
- Research Ethereum Gitter Channel Sometimes Discusses CASPER
Tendermint is a proof-of-stake consensus protocol developed by Jae Kwon and Ethan Buchman. I have seen it implemented in Eris with an Ethereum VM backing.
A Good One Liner for a CASPER vs Tendermint Comparison
“Tendermint favours consistency over availability, Casper favours availability over consistency (see the CAP theorem). Tendermint doesn't punish online validators for potentially censoring potentially-actually-just-offline validators.”