Drivechain
Drivechain is a proposed Bitcoin sidechain design by Paul Sztorc that would let miners custody pegged bitcoin through long hashrate-voted withdrawals and would let those miners collect sidechain fees through blind merged mining. The design is specified mainly as BIP 300 (hashrate escrow) and BIP 301 (blind merged mining). Neither BIP is activated on Bitcoin mainnet, and consensus change proposals implementing them have not been merged into Bitcoin Core.
BIP 300 introduces hashrate escrow outputs that lock bitcoin to a named sidechain. Withdrawals are proposed as compact commitments. Miners then vote in coinbase signals over a long period measured in months. If enough cumulative work supports a withdrawal proposal through the voting window, the escrow releases mainchain bitcoin to the withdrawal destinations. BIP 301 describes blind merged mining, in which sidechain block producers compete to pay Bitcoin miners for inclusion of a sidechain tip commitment without requiring those miners to fully validate the sidechain. A Bitcoin Core pull request attempting BIP 300 consensus logic (PR 28311) was opened as a work in progress and later closed without merge. No BIP 300 or BIP 301 rules are enforced by Bitcoin mainnet nodes today.