On gershon's YouTube channel is an an interesting example of Gnash's flexibility (and what you can do with some sideways thinking):
Gnash is used with some lua bindings to render a flash movie inside a 3-D game. This makes it possible to use any SWF as an interactive UI that can be developed and tested outside the game - even in a web browser.
The Adobe Creative Suite, the most widely-used tool for creating Flash movies, has long used a secret proprietary format known by its extension "fla" to store projects.
These files, if they represent the current state of a project, must contain more than enough information to compile a SWF, but because the format is closed and secret, free software programmes cannot use them.
The swfmill project converts between a special dialect of XML and SWF files. As well as being used by many people for linking together existing SWF resources, it also happens to be useful for changing SWF files at the lowest possible level, giving access to every single property and element of the bytecode.
Gnash, the GNU SWF player is a free software alternative to Adobe's Flash player. Gnash can play most Flash movies up to SWF version 7 and a large proportion of SWF versions 8 and 9. Gnash is extensible, flexible and - unlike the proprietary version - grants users full control.
Gnash allows you to save videos and other media files, can render a SWF to video, and produce screenshots. You can use Gnash to do what you want, not just what the content provider wants.