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:
  1. Simplified the js architecture.
  2. Updated to SWFAddress 2.4 and JQuery 1.41
  3. 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:
The case against html
Traditional html and javascript websites have many limitations: 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.