NEM is a cryptocurrency and blockchain platform that allows multiple ledgers on the same blockchain. NEM Smart Assets are used to create mosaics for any asset. Transaction fees are paid with NEM's native currency, XEM. NEM originally began as a community-oriented cryptocurrency that was built from the ground up in the Java programming language.
NEM's goal is to achieve widespread distribution through improved scale and speed. It pioneered several blockchain features such as its proof-of-importance (POI) consensus algorithm, encrypted messaging, a unique reputation system, and multi-signature accounts.
NEM is also developing a commercial blocckahin called Mijin, that is currently being tested by several companies and financial institutions.
In early 2018, approximately $400 million worth of XEM were stolen from a Japanese exchange called Coincheck, that was the victim of huge hack. The exchange failed to implement proper security for this coin protocol, and the hackers only stole XEM coins as a result. Instead of creating a fork to deal with this issue, NEM set up an automated tagging system that flagged these funds. NEM then stopped tracking these stolen coins

Ravencoin is a blockchain created by the owner of Overstock.com. It is a use case specific blockchain for the declaration of ownership of digital assets. Ravecoin is a fork of Bitcoin, and was originally funded by Medici Ventures, a blockchain investment fund owned by Overstock.com.
Ravencoin's name is inspired by the use of Ravens in sending messages, and its blockchain is designed to carry statements of truth about who owns what asset. The developers created a new consensus algorithm called x16r to solve the problems of centralized ASIC mining. The algorithm is unique in that it consists of 16 different hashing algorithms whose order are randomly changed.