A popular SQL Database, recently made open source.

MySQL is something of a cross between a normal Relational Database and a simple filesystem. It's missing a number of features, such as transactions, triggers, subselects, and foreign keys, but it's about as fast as you can get for pure read speed.

A commonly used tool for MySQL is phpMyAdmin a php driven front-end.

MySQL web page: http://www.mysql.com

phpMyAdmin: http://phpmyadmin.sourceforge.net