Dadabik: open source, suitable for basic front-ends, not actively-developed (latest version released in 2007), demo: http://www.dadabik.org/index.php?function=show_demo
Appgini: commercial (free trial limited to 4 tables per project but doesn't expire), more sophisticated (user management, images, uploads, ... Etc), actively developed (latest version released in November 2009), demo: http://bigprof.com/demo
In short, use dadabik if all you need is a simple CRUD-style database front. Use appgini if you need a more demanding application.
Disclaimer: I'm the developer of AppGini. So, my opinion could naturally be biased towards it, but I tried to provide links above for you to check for yourself and decide what you think is more suitable for you. Please feel free to contact me for any questions at http://bigprof.com/appgini/support-request