Adobe AIR is a runtime. Great tool for those fluent in XHTML/CSS/Javascript/Actionscript to deliver apps for desktop.

If you are a web developer and want to leverage on your existing knowledge to target desktop market, AIR is the way to go.

You dont need Flash/Flex to build AIR apps. The Air SDK is available cost free at adobe.com/products/air/tools/sdk/ Or you can use aptana.com/air

A comparable open source tool: titaniumapp.com