Update: SWIFT has become Lightningbeam. Much of this page refers only to the old version.
SWIFT (which stands for "ShockWave Is Free Territory") is a free, open-source alternative to Adobe Flash. It is written in Python, and uses PyGTK for a GUI, swfc for compiling, and Cairo for image processing. It has the ability to export to HTML5 as well as .swf, allowing for viewing on non-Flash-compatible devices (such as the iPhone or the Kindle), and can pack all resources into a single HTML file for portability. Swift supports ActionScript, allowing for interactive content creation.
I did some more research and found that, although there was no graphical program to do so, there was a text-based one called SWFC. I did some experimenting with it and found that yes, it worked quite well. But it wasn't very easy to use. So, I figured, "Well, I'll just write a GUI for swfc then."