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.

Bitcoin Gold (BTG) is a cryptocurrency that began in 2017 as a hard fork of the Bitcoin blockchain. BTG was created to reduce the monopolizing power of dedicated ASIC mining operations within the original Bitcoin network. Bitcoin Gold mining can be done by anyone with a standard computer and provides greater decentralization to the system. The hard fork that created BTG was meant to combat the disproportionate influence and competitive advantage of professional miners.

Nimiq is a censorship-resistant cryptocurrency that is designed to run in the user's browser. Nimiq's focus is on usability and the browser first approach allows coin holders to participate in their payment network more easily. Nimiq uses a Merkle-based accumulator to store accounts and balances, and has a Non-Interactive Proofs of Proof-of-Work consensus mechanism.