Stacks is an “open-source blockchain network that leverages the security and capital of Bitcoin for decentralized apps and smart contracts.” It extends the functionality and opportunities for developers to create decentralized apps (dApps) and smart contracts on the Bitcoin blockchain.
It was once known as Blockstacks. Blockstacks was first presented in Y Combinator in 2014. The Blockstack was a block-chain based, a decentralized Internet platform that allowed users to completely own and control their personal data. Blockstacks was the first company to be SEC (Securities and Exchange Commission) to receive approval for selling digital tokens. It was renamed Stacks and launched its first version in 2018. STX 2.0 launched in 2020.
Stacks uses Clarity as its programming language and has a unique consensus mechanism called proof of transfer (PoX). It also has a native token called STX.
Stacks (STX) Token
The STX token executes Clarity smart contracts on the STX network. Token holders also receive Bitcoin rewards for stacking their STX tokens. To stack a token, a user must be able to run a full node, lock up STX coins, and periodically publish to the STX blockchain. Stacking more tokens results in more Bitcoin rewards.
Proof of Transfer
Stacks uses a unique consensus mechanism called proof-of-transfer (PoX). The PoX is also the first consensus mechanism to use two independent blockchains. It reuses mined Bitcoins to prove the work done to a node, making it more energy-efficient than regular proof-of-stake or proof-of-work mechanisms.
Images 1 & 2 are credited to: https://www.stacks.co/learn/introduction