While Ripple has been around since 2004, the implementation that we are discussing, which has an internal cryptocurrency and transactions that are confirmed and applied to a shared ledger via a decentralized cryptographic consensus process, has only been around since December 2012.
If you frequent coin market cap and sort on volume, you will see that it is usually in the top three cryptos by volume.
Ripple uses a globally shared ledger, which is based on a radix-16 Merkle tree. Ripple's ledger is a different type of structure from the blockchain, but they are both secured with cryptography (Think of how both gasoline powered cars and diesel powered cars are both still automobiles, even though the engine designs are different, or how propeller planes and helicoptors are both aircraft, if you want an example with more divergence in technology).
With Ripple, each account has a public address and a private secret, which is used to sign transactions cryptographically. The validators use cryptography to ensure that only properly signed transactions are applied to the ledger. Since cryptographic mechanisms and data structures are at the heart of Ripple, it is a cryptocurrency.
The source is completely open under one of the most permissive licenses around (the ISC license). This applies to the source for everything you need to fork a complete ecosystem (libraries, web client, wallet vault, etc) in addition to the core server, rippled.
The collection of repositories is found at https://github.com/ripple and the core server itself is at https://github.com/ripple/rippled
The Ripple source is open enough that the project has already been forked multiple times (by Stellar and some projects in China).
If you want to learn more about how Ripple works, the best place to start is with the white papers:
https://forum.ripple.com/viewtopic.php?t=4301
Start with the primer and then either move to the Gateway paper or the Consensus paper depending on whether you are more interested in how people interact with the system or the algorithm underpinning consensus.
thanks for this explanation, i learn about crypto everyday