What is it?

It's a framework that allows you to create flash or flex websites with all of the benefits of an html website.

You can see working examples here.

Update:	SWFSEO 1.94 is now available for download.
Changes:	Simplified the js architecture. Updated to SWFAddress 2.4 and JQuery 1.41 Fixed versioning bug fix in download zips

SWFSEO Capabilities - Search Engine Friendly, Easy Page Tracking, Powerful Preloading, Dynamic Navigation

The benefits of using the SWFSEO framework:

Search Engine Friendly
When built correctly, all text and images used on your flash website will be visible to search engines. There is only one version of your content to maintain. Your "altContent" is your website's actual content.
Easy Page Tracking
All "page views" can be tracked with one simple function and your own choice of tracking technology.
Powerful Preloading
UltraLoader is a very robust preloader that can preload any kind of asset. Once assets are loaded, they are grouped and organized so they are easy to access or even loop through.
Dynamic Navigation
Create as many navigation buttons as you'd like, and as many or as few levels of sub navigation as you'd like. Navigation can be positioned any way you want. There are even some simple presets that can be used. SWFAddress is used for deep linking and history control.
Scrollable Flash
Make your flash site as big as you want. Optional scrollbars can appear when your flash site exceeds the browser's size. (* ie6 uses custom flash scrollbars, all other modern browsers use browser scrollbars)

The case against html
Traditional html and javascript websites have many limitations:

Browser Incompatibles
A frontend developer probably wastes anywhere from 20-60% of their time tracking down and fixing browser based bugs. This time could be used more productively.
Linear Experience
The user experience is very linear in nature. Users click and wait for the next page to load. Transitions are very limiting and motion is very limiting. While the advent of "web 2.0" has improved the user experience, "web 2.0" pales in comparison with the capabilities of flash. And ironically, "web 2.0" introduced many of the same limitations that plagued flash websites.
Font Limitations
The number of fonts that can be easily and safely used in html is very small. In order to overcome this limitation, many developers create text as images.
Lack of Video support
Until HTML 5 becomes routinely supported by all browsers, video content will be displayed with either silverlight or flash.

With use of the SWFSEO framework, all websites could arguably be built as flash websites. However, html websites should not be abandoned. Websites such as this one work perfectly well in html form. Nonetheless, if you would like to build, "cohesive web experiences" or "applications for the web", flash is the logical choice.