Here is a small list of Open Source Flash Projects. Tell me if you know more.
FFIE
Alternative for Macromedia Flex
http://www.fluidflashinterfaces.com/
Laszlo
The development and delivery platform.
http://www.openlaszlo.org/
Flash For Linux
Development environment for Macromedia Flash,
http://f4l.sourceforge.net/
AS Development Tool (asdt)
A plugin for the popular Eclipse platform to work with ActionScript 2 files
http://www.asdt.org/
JavaSWF2
Set of Java packages that enable the parsing, manipulation and generation of the SWF.
http://www.anotherbigidea.com/javaswf/
Ming
SWF output library and PHP module
http://ming.sourceforge.net/
SSWF
The library which enables a programmer to easily create an SWF file.
http://sswf.sourceforge.net/
AsUnit
Unit Test Framework for Macromedia Flash ActionScript 2.0
http://www.asunit.com/
GPLFlash
GPL licensed flash player.
http://gplflash.sourceforge.net/
MTASC
ActionScript 2 Open Source free compiler
http://www.mtasc.org/
Flash Ant
Command-line Flash Compiler
http://www.flashant.org/
Flirt
SWF rendering library.
http://flirt.sourceforge.net/
Swfmill
Tool to process SWF files. It can convert SWF from and to an XML-dialect. xml2swf, swf2xml, libxslt-based XSL transformator etc.
http://iterative.org/swfmill/
SolVE
Local Shared Object Viewer/Editor
http://solve.sourceforge.net/