MySQL - The world's most popular open source database
Redis - Redis is an open source in-memory data structure project implementing a distributed, in-memory key-value database with optional durability.
PostgreSQL - PostgreSQL is a powerful, open source object-relational database system.
SQLite - SQLite Home Page
PouchDB - Open-source JavaScript database inspired by Apache CouchDB that's designed to run well within the browser
Oracle Database 12c - Simplify database management and automate the information lifecycle with maximum security.