Peercoin (formerly PPCoin) is an altcoin that was one of the first to combine the Proof-of-Stake and Proof-of-Work mechanisms.

Proof of Stake is a consensus algorithm in which the right to create blocks depends on the number of coins locked by a participant rather than on computing power.

Proof of Work is a consensus algorithm in which the right to add a block and receive a reward depends on the amount of computational work done to find a hash.

Proof of Activity is a hybrid consensus algorithm that combines the Proof of Work and Proof of Stake mechanisms to increase the security and resilience of the network.

Proof-of-Burn is a consensus algorithm in which a participant irreversibly destroys a portion of coins in order to earn the right to create blocks and claim a reward in the network.