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.

Eternal is a Japanese cryptocurrency project that consists of Eternal Coin (XEC) and Eternal Token (XET). The project appears to be primarily focused on remittance payments, but can also be used as a medium of exchange for other purposes. XEC holders receive weekly dividend payments, and can only be traded through the company's authorized exchanges. XET was created to allow users to trade XEC on other crypto exchanges. 1 XET=10 XEC.

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.