Qtum is an open-source blockchain that positions itself as developer-friendly and combines technologies from both Bitcoin and Ethereum networks, providing a platform for DApps. It was launched in 2017 by Patrick Dai, Jordan Earls, and Neil Mahi.
The founders of Qtum applied Bitcoin’s UTXO model, accounting system, and Ethereum’s Virtual Machine and account model, a smart contract system, to their blockchain. Account Abstraction Layer (AAL) permits co-existence of the two which amplifies abilities of the network. AAL works by moving, or "abstracting" the account model and adapting it to work on top of Qtum's UTXO. However, it uses a different (to Bitcoin and Ethereum) consensus algorithm for security — Proof of Stake. Qtum’s Proof of Stake deploys the Qtum Core wallet which generates rewards for staking and submitting blocks. Initially, QTUM was an ERC20 token which was then mostly swapped to the Qtum mainnet token by its holders. Currently, the same swap is not available.
In April 2021 Qtum produced a hard fork called FastLane which then decreased an average block time to 32 seconds. It has also recently launched an offline staking opportunity which permits a delegation to a super staker by a non-custodial address.