Having a richer UI than the HTML can provide while still keeping the great deployment model of HTML (or lack of, you don’t deploy anything) is what brought us semi-solutions like AJAX (helping in the interactivity department) and RIA platforms like Adobe AIR and Microsoft Silverlight.

Actually, there was one sorta-kinda competitor here since the end of 2006: XBAP or XAML Binary Applications (at least I think that’s what it stands for). XBAP is a way to bring your WPF application into the browser. You get all the rich interactivity of WPF and simple deployability of Web based solution.

Except that the XBAP sucks, big time. It conforms to the .NET security model and naturally XBAP falls into the “Internet zone” which basically means nothing will work. In the end XBAP is useful in the Intranet scenarios and even there with a few issues.

When Silverlight (SL) 1.0 came out I was really looking forward to its successor, version 2.0 which was supposed to bring .NET CLR into the mix (SL version 2 beta 1 just came out a week ago). SL is a smaller subset of WPF and .NET with added benefit of a lot smaller download size and portability – runs inside all major browsers on Windows and Mac OS X (and even on Linux as soon as Mono guys finish the porting). SL uses different security model and thus is actually useful for (shocking) network-enabled Web applications. Microsoft almost ruined even SL – initially the plan wasn’t to have Socket support in the SL, but after many protests from developers Socket support is now present in 2.0 beta 1.

If you ask me, XBAPs are obsoleted by SL. In Intranet scenarios, I’d just use desktop WPF applications while for Internet scenarios SL is a way to go.

Additionally, Silverlight is revolutionary as it brings the .NET Framework into one other major platform besides Windows – Mac OS X.