OrientDB - OrientDB - The World's First Distributed Multi-Model NoSQL Database with a Graph Database Engine.
PostgreSQL - PostgreSQL is a powerful, open source object-relational database system.
MySQL - The world's most popular open source database
ArangoDB - A distributed open-source database with a flexible data model for documents, graphs, and key-values.
SQLite - SQLite Home Page
RethinkDB - The open-source database for the realtime web