Everyone is offering Application development as a service!
AppJet is the easiest way to create a web app. Just type some code into a box, and we'll host your app on our servers.http://appjet.com/
Bungee Connect is the most comprehensive Platform-as-a-Service (PaaS) — significantly reducing the complexities, time and costs required to build and deliver web applications.http://www.bungeelabs.com/
Coghead is a 100% web-based system that allows knowledge workers to create their own custom business applications. There’s never any software to install or servers to maintain. Just think it, build it and share it!http://www.coghead.com/
Google App Engine
Google App Engine enables you to build web applications on the same scalable systems that power Google applications.http://code.google.com/appengine/
I was going to add more but got bored after reaching G. Now I'm just waiting for that meta web application development environment that integrates all the above with a RESTful API. lol...