PostgreSQL Database Server 8.4.4.1 - Powerful, open source relational database system. (Free)

PostgreSQL is a powerful, open source relational database system. It has more than 15 years of active development and a proven architecture that has earned it a strong reputation for reliability, data integrity, and correctness. It runs on all major operating systems, including Linux, UNIX (AIX, BSD, HP-UX, SGI IRIX, Mac OS X, Solaris, SunOS, Tru64), BeOS, and Windows. PostgreSQL Database server already embedded a useful GUI - PGadmin. If you want to import MS Access or other formats to PostgreSQL, you can install a Mac OS X GUI Navicat PostgreSQL ( http://pgsql.navicat.com ).

PostgreSQL is an open-source descendant of this original Berkeley code. It supports a large part of the SQL:2003 standard and offers many modern features:

1. complex queries
2. foreign keys
3. triggers
4. views
5. transactional integrity
6. multiversion concurrency control

Also, PostgreSQL can be extended by the user in many ways.

Installation guideline for PostgreSQL Mac OS X version.