David Temkin (Laszlo's CTO), inspired by Gmail, writes:

"It's interesting to think of RIAs [Rich Internet Applications]as belonging to three different categories, each analogous to an operating system:

• Unix-style RIA: Gmail is a great example of this. It's essentially text-only, with keyboard equivalents. It's reminiscent of Pine or vi, particularly with regard to how keyboard shortcuts work. The emphasis is on speed, not friendliness -- it's best for geeks and most likely designed by geeks (and I mean that in a nice way).
• Windows-style RIA: Oddpost, another rich Web mail service, is a perfect example of this -- a Windows-style UI delivered into a Web browser. This can be done with DHTML heroics (as is Oddpost), or with Java. Here's a comparable example built with Laszlo. The look and feel of these applications is essentially a duplicate of the "classic" Windows desktop look and feel. Users new to these applications can lean on their familiarity with Outlook and similar applications, but they don't reflect what we've learned on the Web about UI -- very little linking, very little contextual "content" or media.
• Mac-style RIA: Here I'm talking about the visually differentiated, smooth/animated interaction often associated with Mac OS X (or with Flash), but used in the context of a Web application. These applications as a category represent the attempt to blend the best of the Web with the best of applications. Most of Laszlo's deployments and demos fall into this category."

07/08/04 update: I didn't know the guys who do Oddpost came from the defunct Halfbrain.