Almost all of them are obvious scams—including many which purport to have a large market cap. This article aims to list only the most relevant cryptocurrencies in terms of novel technological advancements or strong engineering teams, or due to widespread awareness thereof.
Direct, low-level scams should not be listed here.
First on-chain alternative.
An altcoin based on an old snapshot of Bitcoin's blockchain (2017 Aug 1) with replay protection and an increased block size limit of 8MB.
An unusual emergency difficulty adjustment algorithm causes significant periods of hyperinflation. Significant miner centralization; often a very low hashrate.
Major proponents deliberately attempt to confuse new users into thinking BCH is Bitcoin.
First cryptocurrency that implemented Satoshi's BitDNS idea.
Essentially the first real altcoin. Still under active development.
First merged-mined altcoin.
Introduced the X11 algorithm, which is just a composite function of multiple hashing algorithms.
Had a significant failure mode in the beginning which equated to a majority premine by a small number of Amazon EC2 customers. This means their Master Node algorithm has been in a failure mode from the beginning.
Cryptocurrency Mining For Dummies
Majority premine sale.
Used to be known as just "Ethereum" and "ETH" until the Ethereum Foundation split off an altcoin using their trademark.
Types of Cryptocurrency
An altcoin of Ethereum Classic which split from ETC's blockchain in order to refund the Ethereum Foundation's members' money when the DAO was exploited.
Regular hardforks to bail out larger losses by e.g. ETH foundation.
Source of the ICO bubbles. Multiple client implementations which fail against each other in terms of consensus errors regularly.
Requires multiple months of time to sync to eth blockchain. Contract-building tools interpret input incompatibly.
Originally meant to be a CPU-friendly "silver" to Bitcoin's "gold", the early SCRYPT parameters, it was discovered later, led directly to GPU, and then ASIC-mining almost from the start.
The most successful implementation derived from the Cryptonote codedrop.
Uses Ring Confidential Transactions.
First cryptocurrency that implemented the zerocash protocol.
Large "Founder's Reward" which is paid out over the first few years of mining to people including Roger Ver.
First cryptocurrency that implemented the zerocoin protocol which also makes it the first useful Zero-knowledge proof based anonymous cryptocurrency.
First that implements Merkle Tree Proof of Work (MTP).