With Prism, you can capture your Facebook session into an SSB, for example, and then launch it from an icon on the desktop, just like native software. The site appears in its own window, without any extraneous bookmarks, menu bars, or navigation buttons.

"It's still a Web application, and it's still running on the Web," Finkle explains. "Prism is just a different way to view that application."

That seemingly trivial distinction can make a big difference. After a few hours, it's easy to forget that an application running in Prism is hosted on the Web and not the local machine. By shedding the traditional browser UI, Prism offers an increased level of user engagement that is particularly attractive for Web applications that displace traditional OS-native software.

"Personally, I run my Web mail and calendar in Prism and use a Greasemonkey-like script to pop up OS alerts for incoming mail and meeting alerts," Finkle says.

And users can often install Prism applications the same way they would other desktop software. For example, Ubuntu 8.04 offers a number of Prism SSBs in its standard software repositories.

Getting creative

While Prism's SSBs are really just stripped-down browser windows, however, Adobe AIR takes the concept of stand-alone Web apps a step further. AIR combines an HTML rendering engine with Flash, ActionScript, and a local storage mechanism. Together, these components allow applications built with Web technologies to offer all the luxuries of traditional desktop software.

Users download and install AIR applications using Adobe's custom installer and launch them from icons, just like native applications. Once they're running, they are fully integrated with the desktop. They can open windows or hover above the desktop as widgets. They can even manipulate local files. With the rich graphic capabilities of Flash, there's little to indicate that they were built with Web tools and not C++.

In a sense, AIR is the opposite of Microsoft's Silverlight strategy. Where Silverlight applies concepts from the Windows Presentation Foundation to RIAs, AIR allows developers to migrate traditional Web technologies to the desktop.

To Adobe's Rowe, the transition is a natural one. "The Web model has proven itself. It's possible to make massively scalable, robust applications -- like Amazon.com -- using this model," he says.

In fact, the Web model has many advantages. Because they are standards-based, Web applications are inherently cross-platform. The familiar Web tools and languages also allow rapid application development, without re-inventing the wheel to achieve basic UI conveniences.

Perhaps equally important, AIR applications are meant to look good. "Adobe is really the leader at working with creative professionals," Rowe says. The maker of Dreamweaver, Flash, and Photoshop, Adobe now hopes to bring the aesthetic expertise of artists and Web designers to bear on the software development process, an area where design is too often neglected.

"Some of the highest-value designs and the most impressive experiences I've seen have been on the Web," says Rowe. "Software design on the Web really integrates designers better. We wanted them to be able to take those skill sets and create applications outside the browser."