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.

Fiii Coin is developing an ecosystem designed to promote the wide spread adoption of a variety of cryptocurrencies. Their payment terminal will be compatible with wide range of cryptocurrencies, and will be comprised of a wallet, exchange, and DApp development plugins. The Fiii blockchain has a Delegated Proof of Capacity (DPoC) consensus mechanism.

Sphere is a smart contract platform and peer-to-peer payment network. The network has a hybrid PoW and PoS consensus mechanism and is powered by the native SPHR token, which can be swapped for an ERC20 token over the Ubiq smart contract platform.