SWF (/ˈswɪf/ swif) is an Adobe Flash file format used for multimedia, vector graphics and ActionScript. SWF files can contain animations or applets of varying degrees of interactivity and function.
Currently, SWF is the dominant format for displaying "animated" vector graphics on the Web. It may also be used for programs, commonly browser games, using ActionScript. (Source: Wikipedia)
How to view .swf files? Simple. Just drag and drop into your web browser.