DBeaver - DBeaver - Universal Database Manager and SQL Client.
IBExpert - IBExpert website
MySQL Workbench - MySQL Workbench is a unified visual tool for database architects, developers, and DBAs.
FlameRobin - FlameRobin is a cross-platform, open-source database administration tool for Firebird DBMS.
HeidiSQL - HeidiSQL is a powerful and easy client for MySQL, MariaDB, Microsoft SQL Server and PostgreSQL. Open source and entirely free to use.
RazorSQL - RazorSQL is an SQL Editor and SQL database query tool for macOS, Windows, Linux, and Mac OS X.