PostgreSQL - PostgreSQL is a powerful, open source object-relational database system.
Datomic - The fully transactional, cloud-ready, distributed database
MySQL - The world's most popular open source database
Google Cloud Datastore - Cloud Datastore is a NoSQL database for your web and mobile applications.
MariaDB - An enhanced, drop-in replacement for MySQL
Datahike - A durable datalog database adaptable for distribution.