Sovrin project. Uses a Permissioned blockchain which allows it to do away with mining as an incentive and instead directly build a Distributed Ledger Technology which stores Distributed Identifiers (DIDs) and maps them to claims. Removal of mining frees up resources and increases network throughput. Interesting Key Management aspects, including revocation. Contrasts with Ethereum uPort – which is permissionless and public. Neat design, but will face adoption problem as it is unhitched from bitcoin/ethereum.

Click to access Sovrin–digital-identities-in-the-blockchain-era.pdf

Click to access The-Technical-Foundations-of-Sovrin.pdf

DPKI – Distributed PKI. Attempts to do reduce the weakness of a centralized certificate authority as compromising that cert authority affects each of its issued certificates. This concept is built out and used in Sovrin. https://danubetech.com/download/dpki.pdf

Remme. Remember me. An approach to SSL based logins. Modifies SSL.
Used an EmerCoin implementation as mvp and Ethereum blockchain. EmerCoin: https://emercoin.com/content/EMCSSL.pdf . Adoption problem here is change in behavior of each browser and mobile app. https://medium.com/@alexandermomot/passwords-are-crap-6ed4e97bffa7

Sidechains. Original proposal was to free up resources for when trust is established, to reuse blockchain technology and to establish a two-way peg between the sidechain and the blockchain. https://www.blockstream.com/sidechains.pdf
https://bitcoin.stackexchange.com/questions/32367/mining-on-pegged-side-chains

Coco Framework. https://github.com/Azure/coco-framework

HyperLedger – Linux based framework for developing blockchains software. Provides a DLT and uses Intel SGS extensions. (Intel+Microsoft+Linux foundation). Uses a replicated state machine model with each validating peer independently adding to its chain after reaching consensus on order of txns with other peers using Practical Byzantine Fault Tolerance or Proof of Elapsed Time. https://software.intel.com/en-us/blogs/2017/08/10/collaborating-with-microsoft-to-strengthen-enterprise-blockchains . Related – https://stackoverflow.com/questions/36844827/are-blocks-mined-in-hyperledger

A comparison link – https://stackoverflow.com/questions/41690983/different-between-various-blockchain-protocols