Eclipse SQL Client for database querying/browsing any JDBC compliant database. It supports plugins with specialized functionality for individual databases (Oracle, DB2, MySQL, PostgreSQL, Sybase, Informix) and can be extended.
Vela is a Open Source SQL and PL/SQL client software for Oracle database with a graphical user interface developed using Java Swing. It is a Front-End tool for a Oracledeveloper. It supports most of the common developer tasks.