TOra is an open source database administration and sql tool for Oracle. With TOra you can perform virtually any administrative task on your Oracle database servers - anything from user and security management to server tuning.
It's schema browser together with the sql editor is an ideal tool for both developers and database administrators.
TOra handles multiple connections and it's advanced sql editor includes code completion and syntax highlighting - and for performance it displays your execution plan. A project that is a worthy competitor to the commercial products.