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.

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.

Energi Coin is a Proof-of-Stake (PoS) cryptocurrency that combines smart contracts, decentralized governance, and a self-funding treasury. Energi was founded by Tommy World Power, with the goal of creating a more sustainable cryptocurrency that had the potential for mass adoption. Energi Coin's funding model is a built-in to the protocol and fuels the growth of the project. Aa portion of freshly-mined coins is assigned to the Treasury. The treasury allows the project to fund not only development, but also support, operations, and marketing. The founder, Tommy World Power personally funded the initial development of the project. Energi is currently shifting to a Solidity-based smart contract platform that will combine all of Ethereum’s existing capabilities with Energi’s unique governance and treasury model.