RethinkDB is the first open-source, scalable JSON database built from the ground up for the realtime web. It inverts the traditional database architecture by exposing an exciting new access model – instead of polling for changes, the developer can tell RethinkDB to continuously push updated query results to applications in realtime. RethinkDB’s realtime push architecture dramatically reduces the time and effort necessary to build scalable realtime apps.

RethinkDB Horizon is an open-source developer platform for building realtime, scalable web apps. It is built on top of RethinkDB, and allows app developers to get started with building modern, engaging apps without writing any backend code.

Horizon consists of three components:

Horizon server: a middleware server that connects to/is built on top of RethinkDB, and exposes a simple API/protocol to front-end applications.
Horizon client: a JavaScript client library that wraps Horizon server’s protocol in a convenient API for front-end developers.
Horizon CLI: a command line tool, hz, aiding in scaffolding, development, and deployment.