Ingres
Ingres
® is a mature, high-performance relational database solution. It offers scalability, integration and flexibility to leverage information resources across a wide range of platforms, including Linux, UNIX, Windows and OpenVMS. Reliable and cost effective, it supports mission-critical applications in small to medium-size businesses and high-volume deployments in large scale enterprises.
http://opensource.ca.com/projects/ingres/EnterpriseDB
EnterpriseDB is an enterprise-class relational database management system (RDBMS) that is built on PostgreSQL, the world's most advanced open source database. EnterpriseDB is compatible with most Oracle applications, reliable and scalable enough for high-volume, mission-critical enterprise use, and surprisingly affordable.
http://www.enterprisedb.com/products/index.do
Mysql
The World's Most Popular Open Source Database
http://dev.mysql.com/
Postgresql
The world's most advanced open source database.
http://www.postgresql.org/