FirebirdSQL

Firebird is an open source RDBMS server that uses SQL for inserting, selecting and updating data. It's very fast, capable, flexible, and runs on UNIX, Linux, Mac and Windows platforms.

Quick Start
Install firebird from your distribution. /etc/init.d/firebird2.0-super start (actual command may vary depend on the flavor and version installed)
 * Start firebird on your local computer with

isql-fb (or /opt/firebird/bin/isql) sql> connect /home/user/mydatabase.fdb user sysdba password masterkey; sql> show tables; sql> select 'enter a valid sql command here!' from rdb$database;
 * Build up a connection to firebird:

gsec -user sysdba -password masterkey gsec>modify sysdba -pw newpassword gsec>quit
 * Change the password of sysdba

gsec -user sysdba -password masterkey gsec>add newuser -pw newpassword gsec>quit
 * Create a new database user

GUI's include

 * FlameRobin

Install on debian
It seems to official packages in debian are broken (as for version 1.5 and 2.0). You can find a script to install firebird in debian (site is in Spanish)