MySQL - The world's most popular open source database
MongoDB - MongoDB (from "humongous") is a scalable, high-performance NoSQL database.
PostgreSQL - PostgreSQL is a powerful, open source object-relational database system.
SQLite - SQLite Home Page
ElasticSearch - Elasticsearch is an open source, distributed, RESTful search engine.
Oracle Database 12c - Simplify database management and automate the information lifecycle with maximum security.