BitcoinDark is a fork of Bitcoin with a poorly defined purpose and use case. BitcoinDark is based on the InstantDEX protocol, a decentralized exchange for BitcoinDark and other cryptocurrencies supported by the project. The platform is also supposed to include a Pegged Asset Exchange (PAX) to allow users to buy and sell pegged assets – including fiat currencies, commodities, ETFs, and stocks.
BitcoinDark is a Proof-of-Stake (PoS) currency that has gained a significant market cap, but the project has failed to show how its vision will be implemented or how it will add value compared to other blockchain projects.

Primecoin is a cryptocurrency based on finding prime numbers. Identifying prime numbers plays a central role in cryptography. Primecoin's unique Proof-of-Work (PoW) consensus mechanism is able to increase transaction speeds and improve energy efficiency.
The network searches for special prime number chains known as Cunningham chains and bi-twin chains, which are of interest in mathematical research.

Flash Coin is a cryptocurrency designed to be used for everyday transactions. Flash's blokchain has a delegate-based consensus model that depends on elected delegates to verify transactions. These delegates elect 25 Miners who create new blocks on the blockchain. Each miner is given a specific time where they can mine a block. The Flash Coin algorithm also introduces a concept called Consensus Height, which refers to the moment when more than half of elected miners have created a block on top of another block in the chain.