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).
DB Copy Plugin is a plugin for the SQuirreL SQL Client (1.2beta6 and 2.0 RC1+) that allows copying database objects (schema def and data) from one session window to another. The sessions can be disparate database vendors (Oracle -> MySQL, for instance).