BigchainDB

vs

LevelDB

PouchDB is a free and open-source JavaScript database inspired by Apache CouchDB. The database is designed from the ground-up to run well within modern web browsers. With PouchDB you can create web applications that works as well offline as they do online. PouchDB achives this by storing data locally, then synchronize it with CouchDB and compatible servers when the user get internet access once again. This is especially useful for applications facing countries and regions with lower quality internet connections or unstable infrastructure.

OrbitDB is free and open-source serverless, distributed, peer-to-peer database for IPFS (Internet Planetary File System). The database is most commonly used for decentralized apps (dApps) and blockchain applications. With OrbitDB, IPFS is used for data storage, while IPFS Pubsub is used to automatically sync databases with peers across the network. Which makes OrbitDB an "eventually consistent database" that uses CRDTs for conflict-free database merges, suited for decentralization of data.

RxDB is short for Reactive Database and is a NoSQL-database for JavaScript Applications like Websites, hybrid Apps, Electron-Apps, Progressive Web Apps and NodeJs. Reactive means that you can not only query the current state, but subscribe to all state changes like the result of a query or even a single field of a document. This is great for UI-based realtime applications in way that makes it easy to develop and also has great performance benefits. To replicate data between your clients and server, RxDB provides modules for realtime replication with any CouchDB compliant endpoint and also with custom GraphQL endpoints.

Redis is a free and open-source, in in-memory data structure store that can be used as a database, cache or message broker. The project is community developed and released under the BSD license. Redis supports common data structures including strings, hashes, lists, sets, sorted sets with range queries, bitmaps, hyperloglogs, geospatial indexes with radius queries and streams.

CouchDB is a free and open-source document-oriented NoSQL database developed by the Apache Foundation. The database is written and implemented in the language Erlang and provides the use of multiple formats and protocols to store, transfer, and process data. With CouchDB you query data with JavaScript using MapReduce, and HTTP for an API. Which can be done across multiple distributed CouchDB instances as the database has the ability to synchronize multiple copies of the same database, across servers.

MongoDB is an open-source document-oriented distributed database built for modern applications. MongoDB uses JSON-like documents with optional schemas and is classified as a NoSQL database. The database is freely distributed under the Server Side Public License, but MongoDB provides commercial version of the database for enterprise-scale applications.