Bitcoin is the first digital currency based on blockchain. It solved the double-spending problem and enabled peer-to-peer transactions on a large scale. Bitcoin was designed to work as a trustless digital currency that would function without government oversight or a central bank.
Bitcoin was developed by Satoshi Nakamoto, whose identity has never been confirmed and has become the subject of great intrigue. Bitcoin builds upon on other cryptographic and digital currency projects that came before it, but its use of blockchain made it more viable. Nakamoto originally released his white paper and open-source software on a cryptography forum. He mined the first block of the Bitcoin chain, called the genesis block in January 2009.
Bitcoins are created as a reward for a process known as mining. One of the core innovations of Bitcoin, is its consensus algorithm, which creates an incentive system that rewards miners for confirming transactions.
Hal Finney, who developed the first reusable proof-of-work system (RPOW), several years before, was the first Bitcoin adopter and received the first bitcoin transaction ever recorded on its blockchain.

Stellar is a decentralized protocol for sending and receiving money, in any pair of currencies, directly on the internet. Stellar enables users to transfer money on their network directly, without banks, and without fees. It was originally created by Jed McCaleb, the founder of Mt. Gox and co-founder of Ripple.
Stellar has its own native coin called Lumens (XLM). All users must hold a minimum of 20 Lumens in order to ensure their authenticity and to maintain a wider distribution and free flow. Users must spend 0.00001 XLM in order to transfer fiat currencies. This provides the network with more liquidity for less popular currency pairs. Lumens are an inflationary currency with a fixed increase rate of 1% per year.
The network uses the Stellar Lumens Consensus Protocol (SCP). Unlike PoW or PoS consensus mechanisms, SCP relies on a Federated Byzantine Agreement (FBA), in which specific groups of nodes are chosen to arrive at transaction agreement. This provides the Stellar network with more decentralized control.
Lightyear.io, a for-profit entity of Stellar, was launched in 2017 as the commercial arm of the company.

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