DigitalNote (XDN) cryptocurrency is currently listed on the number of exchanges against cryptos (BTC or ETH). It emerged in 2015 as a Fair Launch, which did not imply any reward for developers, ICO campaign or premined blocks . Recently, XDN held a swap to the XDN 2.0 network with improved functionality.
Zcash (ZEC) is a cryptocurrency with strong cryptography that is supposed to provide high security and privacy. At some point, Zcash was endorsed by Edward Snowden and Roger Ver. Zcash is a Bitcoin fork and it exists since 2016. The mechanism providing privacy is called zero-knowledge proofs (or zk-SNARKS).
Scry.info (DDD) is an Ethereum-based token of the Scry.info global data aggregator. DDD token is listed on a few exchanges paired against bitcoin and Ethereum. In this abbreviation, “DDD” stands for "distributed data depositary".