A blockless "blockchain" or trustchain

Traditional proof-of-work blockchains are notoriously slow and inefficient, and there have been numerous efforts over the years to make improvements. Some of these efforts have met with at least some success. Some permissioned chains that can use less onerous consensus mechanisms such as the Financial Blockchain Shenzhen Consortium Blockchain OS (FISCO BCOS), the Hyperledger Fabric, or R3 Corda, for example, claim between 1,000 to 6,000 transactions per second (TPS), versus single or double digit TPS for the most popular permissionless chains that use proof of work. Of the permissioned chains, my impression is that Hyperledger is most frequently cited in enterprise case studies. 

Also often mentioned in a performance context is BigChainDB. According to ZDnet, BigChainDB is actually two distributed databases with a consensus protocol that operates between them, a way to add blockchain features to a database. As a result, it offers many database features that are simply absent from blockchains entirely. BigChainDB says it will eventually reach a million writes per second, and claims Daimler, Toyota and VW as customers.

One 2018 improvement being highlighted in the press recently is"blockless" chains that can be used for cryptocurrency, also known as DAG (for directed acyclic graph) chains. 

Coti, a white label currency startup out of Gibraltar, posted a white paper this month that claims its multiDAG Trustchain will eventually validate hundreds of thousands of transactions per second (TPS), compared with a maximum of seven TPS for the bitcoin blockchain. Coti hopes this level of performance improvement and the security features associated with its solution will encourage others to adopt its infrastructure and offer branded versions of its coin.

In this DAG scheme, instead of block-by-block validation, a new transaction acts to validate two previous transactions and then add them to the graph. 

Coti also offers on-chain, decentralized smart contracts it says are comparable to Ethereum's smart contracts, but competitive in performance to other high-performance chains it says must keep smart contracts off chain to stay performant.

Coti's was not the first DAG chain to appear. In a January 2018 Forbes post, Sherman Lee mentioned several other DAG chains, both block and blockless chains.