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The Ripple (payment protocol) is a trust-less transfer technology based on a network of servers that enables trading in different currencies. It is released under the ISC license - ripple.com 
It uses it's own currency XRP. For more information see Ripple on GitHub .
One of the liabilities that Ripple has all to itself is a corporate structure.
Ripple consensus protocol paper was written by David Schwartz , Arthur Britto , and Noah Youngs.
The Ripple Protocol consensus algorithm (RPCA), is applied every few seconds by all nodes, in order to maintain the correctness and agreement of the network. Once consensus is reached, the current ledger is considered “closed” and becomes the last-closed ledger. Assuming that the consensus algorithm is successful, and that there is no fork in the network, the last-closed ledger maintained by all nodes in the network will be identical.
Codius - Smart contracts protocol by Ripple.