A super fast key value store that can use memory or persist to disk. Often used by other systems for caching or event subscriptions.

The ubiquitous open source database. This technology probably powers most of the known web. May mangle your utf8 strings if you don't set the charset and collation correctly.

Arguably the best open source general purpose database (sorry MySQL). Plenty of excellent extensions including GIS.

PouchDB is a library for connecting to CouchDB and also an implementation of the CouchDB protocol inside the browser. Great for browser based editing tools.

This legendary database commands respect. In it’s millionth iteration its rock solid and used by large enterprises everywhere.

A GraphQL native graph database. Dgraph can be used for a simple search index or ramped up into a dynamic schema optional index calculating jugganaut.

Relax, CouchDB is syncing. CouchDB is a document store with a update model that can handle multiple, conflicting versions of the same document. Good for offline sync.