Adobe Air is not so much an application in its own right as a platform which can be used to run other applications. Using Flash, Flex, Ajax and HTML, programs can be designed that run on a range of platforms freeing them from the constraints of the internet. Online applications have seen something of a popularity surge in recent years, and Adobe Air aims to make them as close to traditional hard drive based programs as possible.
There are a huge number of applications available for the Air platform - everything from Twitter clients and eBay tools to agenda tools and media players - and there is a key benefit of using Air. Should you switch from a Windows based PC to a Mac or Linux machine, or frequently work with computer which have different operating system installed, the cross-platform nature of Air means that it is possible to work with the same programs without the need to install a platform-specific version.
After Adobe Air has been installed, don't be confused by the fact that no program shortcuts have been created to launch the tool - you will first need to install one or more Air applications; a good starting point is to pay a visit to the Adobe Air Marketplace at http://www.adobe.com/go/airmarketplace. From here you can browse through a wealth of tools covering all manner of topics.