As feature rich internet applications are becoming more popular every day there are also more and more frameworks to develop such. There are various AJAX frameworks but if you want to build your client application to take advantage of Flash's features you do not that many choices. Adobe Flex is one but it is not free but OpenLaszlo is. It supports Flash and now with brand new version 4 it also has support for DHTML.

I have been playing around with it and it seems to be quite easy to get started with even though I have very little experience with Flash development. OpenLaszlo has an active community around it and documentation is mostly good. Their site has also numerous examples how to use it.

If you think it needs Flash plugin and nobody has it you should know that plugin is available over 95% percent of browsers. That makes it better than Java Applets in sense of availability. Now I only need an idea for my killer application...