If you want to build powerful web mapping applications just by providing a JSON configuration, you might want to try GXP, a brand new and exciting open source Javascript library. It provides a plugin-based architecture leveraging OpenLayers, Ext JS, and GeoExt.
web mapping

The applications of the OpenGeo Suite, such as GeoExplorer, are being built on top of GXP, showcasing the capabilities of the library.

GXP provides functionality for seamlessly editing data through a Web Feature Service (WFS), adding layers to a map, creating styles, building filters and many more.

There is also a good integration with commercial map providers such as Bing Maps, Google Maps, MapQuest and OpenStreetMap. GXP applications can use the Google Geocoder for search and integrate Google Street View and Google Earth.

GXP is being developed on the github social coding platform, so there are plenty of ways for people to contribute to GXP. For more information, please refer to: https://github.com/opengeo/gxp

Below is material presented on FOSS4G 2011 by Bart van den Eijnden from OpenGeo :

Introducing GXP: Webmapping made easy