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
"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