Here’s a nice PHP framework called P4A (stands for PHP For Applications) for those interested in creating web applications quickly. I’ve built a few web applications for work using this framework and I really like how fast you can build things with it. You don’t even need to know much about PHP to get started (I’ve never worked with PHP before I started playing around with this framework). As long as you know some basic object oriented programming concepts you should be fine.
Check out this link for a demo of P4A in action: P4A Web App Demo
You can find more information from their website: http://p4a.crealabsfoundation.org.
I also strongly recommend that you watch these screencasts before you start playing around with it, they’re very helpful: Build your CMS in 10 Minutes, Address Book Demo