SWFTools is an open-source SWF (Flash) library and toolkit I started together with Rainer Böhme and have now been actively maintaining for 7 years.
It contains a multitude of utilities and converters, which can generate Flash files from audio files, video files or text documents (PDF). It also contains disassembler and assembler for AVM1, AVM2 actionscript, as well as a scripting language (swfc) for generating complex animations with just a few lines of code.