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.
CoolSQL is a free database client software. It is better for people who develop applications related to database and manage database. CoolSQL is written by Java, so it can run on the platform where installed the Java Runtime Environment (1.5 or above).
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 Oracle developer. It supports most of the common developer tasks.
SDBC is a MS Access-like database client based on Java swing ui, able to connect to both local and network DBMS. It uses Derby for file-based database and JDBC for SQl-based DBMS.
DBPad is a GUI-based SQL client for relational databases. As long as you have a JDBC driver for your DB, you can use DBPad to view or manipulate your data and metadata of your tables.