Rich Web Clients ..
Since AJAX came along there has been renewed interested in building rich clients for web applications. Even the W3C recently launched the Rich Web Client Activity.
From a technical point of view I could never quite share the prevalent enthusiasm about AJAX (come one, we can do all this with Java Applets/WebStart for a decade now) but recently I came accross a couple of great tools/developments for Rich Web Clients (no, not AJAX):
One is Macromedia's Flex(Wikipedia), a platform and application server that abstracts away a lot of the details of building rich web clients (and the "back" button works :-) ). There's a free trial and a free developer version but it is expensive to deploy. A similar approach is taken by the open source platform Laszlo. Microsoft is appearently also working on a similar system called Sparkle. Here again the focus is to make it easier for designers and application developers to work together.