MongoDB - MongoDB (from "humongous") is a scalable, high-performance NoSQL database.
PostgreSQL - PostgreSQL is a powerful, open source object-relational database system.
Brilliant Database - Create a personal or business desktop database fast and easily using this simple all-in-one database software. Free 30 day trial.
MySQL - The world's most popular open source database
CouchBase - Document-Oriented NoSQL Database
SQLite - SQLite Home Page