The lines distinguishing a web application from a desktop application have certainly been blurred with the adoption of application platforms such as Microsoft Silverlight and Adobe AIR.
Rich Internet Application, or RIA's, are what these applications are called. They run in a browser, and most applications built on these platforms usually communicate with a backend server. That sounds like an internet application. But peel back a layer and you'll see that RIA's have much more in common with their desktop application brethren than your traditional server-hosted internet application. These apps run in a browser, this is true, but they run completely on the client system. Unlike a traditional web app, and much like a desktop app, once started, neither the server or the browser is really necessary. It's so not necessary, that upcoming releases the major RIA platforms plan to include a no-browser mode, so that these apps can run outside of a browser. Right now, as I type, there are .Net development leads out there pondering whether they should build their next app as a Silverlight application or as a smart client app (WinForms or WPF) deployed through ClickOnce. Cross-platform capabilities notwithstanding, the case for ClickOnce and WPF over Silverlight is so strong, it's difficult to understand why there is even an argument. Understanding comes in a word...
Deployment. It's like the four letter word (that's not a four letter word) of software development. Nobody wants to even think about having to actually deploy software. The mere thought invokes headaches. Deployment is so much at the root of these decisions that we should be calling these applications Browser Deployed Applications, or BDA's. A Browser Deployed Application is an application that can be downloaded and launched using any standards compliant browser and runs on multiple computing platforms. More accurate I would say.
The most interesting aspect of this is that over the same period of time that RIA's have come on the stage, deployment of thick desktop based applications has become so much easier than it once was, and hardware virtualization promises that soon we'll see seamless cross-platform capabilities though virtual functionality. Surely, for many applications and target environments, the pain of limited development capabilities that come with RIA's would be much more burdensome and costly than the deployment challenge of today's .Net thick client applications.
The future may indeed be computers with nothing but a browser installed. But that day is not today. Today, users still expect more than that from their computers and their applications. Don't be afraid of software deployment. You just might spend less and get more by stepping out of the browser for your next application.