Gaby is a small personal database manager using GTK+ and GNOME (if available) for its GUI. It was designed to provide straight-forward access to the types of databases a casual user would normally use, while keeping the ability to easily create databases for other needs. It was designed with extensibility in mind and relies heavily on plug-ins.
ToutDoux is a project manager for GNOME. The approach of data manipulation is abstract (database free). It's extensible with plugins. Most tasks are and will be subcontracted with commandline frontends. The file format is XML (including a schema, plugins parameters, and datatables).
KmusicdB is a music information manager for KDE, using PostgreSQL as a backend. You can add your music collection to the database, and view it in a convenient browser. It currently supports the ability to add and edit artists, add and edit titles (with album pictures), and a track editor. The ability to generate reports and statistics, and also to search the database is implemented, as well as creating and opening, backing up and restoring databases. It is highly customizable, and fast. CDDB functionality has also been implemented.
Open Simp-X is a powerful Internet platform for everyone, attempting to change programming for the Internet with sharing database information. It strives for scalablility, reliability, and ease of use. The platform consists of a client/server pair. Security is a top priority, and data transfers are encrypted. Open Simp-X achieves scalability through plugins. Plugins can collect information, manipulate it, and send it back to the database. Writing plugins is easy since they do not have to worry about how to send or receive their information, and can focus on manipulating it. Open Simp-X can be set up to retreive data through a LAN or through a Web server.
Copper is the feature-wise Linux port of the Windows-only software Golden32 by Benthic. It allows developers to view data in a table format rather than in SQLplus, and lets you do select, insert, update, delete, commit, and rollback. It supports Oracle and MySql, and features a tabbed view to manager your queries, syntax highlighting, right-click updates, and a table/column browser.