With Glom you can design table definitions and the relationships between them, plus arrange the fields on the screen. You can edit and search the data in those tables, and specify field values in terms of other fields. It's as easy as it should be.

Glom uses the PostgreSQL database backend but it can not edit databases that it did not create, because it uses only a simple subset of Postgres functionality.

Here are some screenshots, with explanations:
http://www.glom.org/screenshots/

Glom is written in C++, with gtkmm, Bakery, and libgdamm. It uses
Python for calculated fields, with help from pygtk.

More information is at
http://www.glom.org