gameswf is an open source Public Domain library for parsing and rendering SWF movies, using 3D hardware APIs for rendering. It is designed to be used as a UI library for computer and console games.
It is written in C++, and compiles under Windows and Linux, using GCC and MSVC. It currently includes code for rendering with OpenGL.
It is currently being maintained as a semi-autonomous part of my personal tu-testbed project on SourceForge.
The biggest benefit of using SWF as a file format for game UIs is the availability of high quality authoring tools (like Macromedia Flash MX) and the large number of talented designers who have expertise with these tools. The SWF format is not perfectly suited for game UIs, but it's not bad, and my hope is that gameswf will help improve the quality of game UIs while reducing the effort that goes into making them.
I've been looking for something like this for years. Typically, you rebuild a GUI system for each game and you never make an editor, mainly for time / money reasons. And so you waste money and your GUI is never as good as it could be.
Macromedia weren't very understanding when I talked to them about it. "So you want a Flash rendering engine? For the PC? Er..." SVG could be cool one day, but the tools aren't there yet.
Others have done Flash players for games, but this is the first one I've seen that's open source. I haven't tried it out myself, but I have a good opinion of Thatcher's programming skills (plus he's a nice guy), so I have high hopes.