Types of Blockchains

Blockchain is a distributed database which maintains a continuously growing list of data records secured from tampering and revision. These records are stored in the form of data blocks which are added to the end of the database in chronological order. The blockchain is the primary technology behind Bitcoin, where it serves as the public ledger for bitcoin transactions. Many altcoins emerged after the rise of Bitcoin. Blockchain technology is the backbone of all of them. After people had started to understand how the blockchain works, they began using it for other purposes, such as a store of value, identities, agreements, property rights, etc. Ethereum is the biggest innovation after Bitcoin. It provides a way to create online markets and programmable transactions known as smart contracts. Three main types of blockchains exist:

# Public blockchains
Anyone in the world can read, anyone in the world can send transactions to and expect to see them included in the blockchain if they are valid, and anyone in the world can participate in the consensus process – the process for determining what blocks get added to the chain and what the current state is. Public blockchains are open-source. Everyone can be part of them and explore them. These blockchains are secured by the concept of crypto economics – a system of economic incentives and cryptographic verification backed up by consensus algorithms such as Proof-of-Work(PoW) or Proof-of-Stake(PoS). Crypto-economics enable developers to create systems which have certain desired properties such as availability where higher paid fees result in faster transactions or convergence where new blocks can be added to the blockchain, but blocks cannot be replaced or removed.
Examples: Bitcoin, Ethereum
Find a list of all publicly listed blockchains and their market cap here.

# Consortium blockchains
Consensus process is controlled by a pre-selected set of nodes; for example, one might imagine a consortium of 15 financial institutions, each of which operates a node and of which 10 must sign every block in order for the block to be valid. The right to read the blockchain may be public, or restricted to the participants.
Example: R3, Corda

# Private blockchains
Write permissions are kept centralized to one organization. Read permissions may be public or restricted to an arbitrary extent. Likely applications include database management, auditing, and more that are internal to a single company, and so public readability may not be necessary in many cases at all, though in other cases public audit ability is desired.
Examples: MONAX, Multichain

Source: Ethereum Blogpost by Vitalik Buterin

 

Source: coindesk.com, chris skinner’s blog

 

Bitcoin

On 31 October 2008, an anonymous person or a group called Satoshi Nakamoto introduced the idea of Bitcoin. The system is peer-to-peer, and transactions take place between users directly, without an intermediary. These transactions are verified by network nodes and recorded in a public distributed ledger called the blockchain, which uses Bitcoin as its unit of exchange.
Characteristics: consensus mechanism: Proof of Work (PoW); type of blockchain: public blockchain

 

Ethereum

Ethereum is an open blockchain platform which lets anyone build and use decentralized applications which run on blockchain technology. It was introduced by Vitalik Buterin in late 2013 and was formally announced on 25th January 2014. Since then Ethereum has been used as a platform for decentralized applications (dApps), decentralized autonomous organizations (DAOs) and smart contracts.
Characteristics: consensus mechanism: PoW (future plans include moving to Proof of Stake(PoS) algorithm); type of blockchain: public blockchain.

 

Dash

Dash (Digital Cash) is a privacy-centric digital currency with instant transactions and integrated governance system. It is based on the Bitcoin software, but it runs a two-tier network which improves upon it. Dash allows you to remain anonymous while you make transactions. Dash is the first cryptocurrency to implement a system of self-funding through the blockchain.
Characteristics: consensus mechanism: PoW; type of blockchain: public blockchain

 

Lisk

Lisk is a public blockchain and sidechain application platform which aims to provide developers with the tools to deploy decentralized applications. The idea behind Lisk is that every blockchain app will run on its own sidechain, separated from the main blockchain.
Characteristics: consensus mechanism: delegated proof of stake (DPoS); type of blockchain: public blockchain

 

Steem

Steemit is powered by the Steem blockchain, an open source, and publicly accessible database, that records all posts and votes, and distributes rewards across the network. Steemit is designed around a relatively straightforward concept: everyone’s meaningful contribution to the community should be recognized for the value it adds. Steemit aims to support social media and online communities by returning much of its value to the people who provide valuable contributions by rewarding them with cryptocurrency.
Characteristics: consensus mechanism: PoW; type of blockchain: public blockchain

 

Ripple

Ripple is a real-time gross settlement system (RTGS), currency exchange and remittance network based upon the Ripple Labs version of the blockchain. Ripple’s distributed financial technology allows for financial institutions around the world to directly transact with each other without the need for a central counterparty or correspondent. It works with any currency (dollars, euros, yen, etc.), and it settles transactions, including cross-currency transactions.
Characteristics: consensus mechanism: Ripple Protocol consensus algorithm (RPCA); blockchain type: private blockchain