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.

Sharechain is developing a Proof-of-Work cryptocurrency platform. Their network is currently fueled by the Ethereum-based SSS token. Their marketing materials are unclear and do not offer any information about its advantages.