FOSS tools for generating .swf movies

[Michael ODonnell]

I generally detest Flash since its primary application
seems to be as a tool for constructing the elements
(or even the entirety) of extremely annoying WWW pages.

However, I do also admire some of the very entertaining
and useful things that can be done with it when it's used
as the primary delivery medium, so I'm curious about
how one constructs a Flash movie and whether any FOSS
tools are available.  Is it the case that Macromedia
have managed to keep the format proprietary and corner
the market for the development tools?