MySQL - The world's most popular open source database
DBeaver - DBeaver - Universal Database Manager and SQL Client.
PostgreSQL - PostgreSQL is a powerful, open source object-relational database system.
Firebird Maestro - SQL Maestro Group vendors powerful database management and web development tools for MySQL, Oracle, SQL Server, DB2, SQL Anywhere, PostgreSQL, SQLite, Firebird and MaxDB.
SQLite - SQLite Home Page
FlameRobin - FlameRobin is a cross-platform, open-source database administration tool for Firebird DBMS.