PostgreSQL is a powerful, open source object-relational database system running on all major platforms. It supports native programming interfaces for C/C++, Java, .Net, Perl, Python, Ruby, Tcl and ODBC among others.

Features:
fully ACID compliant
full support for foreign keys, joins, views, triggers, and stored procedures (in multiple languages)
includes most SQL 2008 data types, including INTEGER, NUMERIC, BOOLEAN, CHAR, VARCHAR, DATE, INTERVAL, and TIMESTAMP
supports storage of binary large objects, including pictures, sounds, or video
multi-Version Concurrency Control (MVCC)
Highly customisable