HTMLCOIN is a Proof-of-Stake (PoS) blockchain platform focused on enabling the practical applications of smart contracts. The HTML blokchain is a hybrid of Ethereum and Bitcoin, and also combines elements of other blockchain infrastructures.

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.

ZClassic is a privacy focused crytpocurrency that is a fork of ZCash. ZClassic enables a high degree of privacy and anonymity of transactions.The key differences between ZClassic and ZCash are the elimination of the 20% mining fee that are allocated as a "founders' reward" and the removal of ZCash's block limit, that was intended to create scarcity.