Peercoin is the first Proof-of-Stake (PoS) cryptocurrency. It was created in 2012 and is one of the oldest and most reliable cryptocurrency networks in the crypto sector. The protocol was developed by Sunny King and Scott Nadel, both of whom are anonymous. Sunny King also created Primecoin and VEE.
Peercoin’s PoS consensus mechanism is now widely used in the blockchain space, and allows every network participant to be both a miner or an owner. The project is focused on creating a cryptocurrency platform that will be stable, secure, energy efficient, and distributed fairly.

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.

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.