L2_protocols.md

L2 protocols

Trust protocols (not always auditable)

• Full custody (Coinbase)
• 2-of-3 arbitration / DLC
• Threshold multisig (ecash, Liquid)
• Off-chain peg-out tx (statechains)
• Collateralized custody

Payment channels

• Lightning Network
• Pools/factories
• Aggregated coinswaps (Ark)

"SPV" two-way peg protocols

• Sidechains paper
• Drivechains
• Fraud proofs
• Softchains
• Availability sampling

On-chain token protocols

• op_return / on-chain (Omni)
• Off-chain validation (RGB)

Perpetual one-way peg

• Vanilla spacechains
• Fee-burning "two-way" peg

SNARK protocols

• Full on-chain data (zk-sync)
• Bit field data only (zendoo)

Trusted hardware

• Single device (opendime)
• Remote attestation (teechan)

Has potential (may not work)

• Probabilistic payments
• Plasma Cash

Other related topics

• Merged-mining
• Blind merged-mining
• Stakechains
• Proof of publication

Why aren't rollups on the list?

This is a surprisingly uncommon opinion, but I stand by my assessment that they do not fit a useful definition of L2 (i.e. one that excludes extension blocks). Everyone on the L1 has to fully download and validate them and they cannot function an optimally efficient L1 that also uses ZKPs for validation.