MongoDB - MongoDB (from "humongous") is a scalable, high-performance NoSQL database.
PostgreSQL - PostgreSQL is a powerful, open source object-relational database system.
Amazon DynamoDB - Amazon DynamoDB is a fully managed NoSQL database service offered by Amazon.
CouchDB - HTTP + JSON document database with Map Reduce views and peer-based replication
MySQL Community Edition - MySQL :: MySQL Community Edition
Apache Cassandra - The Apache Cassandra database is the right choice when you need scalability and high availability without compromising performance.