Simple ABCI application serving a merkle-tree key-value store. Merkleeyes allows inserts and removes by key, and queries by key or index. Inserts and removes happen through the DeliverTx message, while queries happen through the Query message. CheckTx simply mirrors DeliverTx.

ABCI is Tendermint's Serverside Blockchain API, whilst Tendermint Core is Byzantine Fault Tolerant (BFT) middleware that takes a state transition machine, written in any programming language, and replicates it on manymachines.