If you haven't heard of LyteRAD its a code free environment to build database apps in minutes. Available as a free edition too!
The latest version of LyteRAD is now available on Linux. Though it is not open source, There is a free version available for all uses. What really sets apart LyteRAD on Linux is the ability to build database driven apps with zero code, and ofcourse access to a gallery where you can download many ready to use applications for free.