Flex: http://opensource.adobe.com/wiki/display/flexsdk
They sell a modified Eclipse IDE called Flash Builder but you can also compile and code without it.
I'm curious, please provide link to any capable tool.
Apart from the links 'geeymb' posted, FlashDevelop is a popular free tool to create flash content [flashdevelop.org]
Scribd uses 'pdf2swf' from swftools.org to convert pdfs(Not sure if they still use it. ref: http://www.swftools.org/references.html )
Scaleform depends heavily on Flash[scaleform.com]. Ming library is a nice option to create dynamic swf files on server side[libming.org].
A nice little online editor and compiler can be found here: http://www.victordramba.com/?p=31
Although there are so many nice, robust open source tools built around Flash, i haven't heard of Adobe actively promoting any of them.
That statement is wrong. Anyone can create tools that can 'create' and/or 'run' swf files. Adobe itself provides Flex SDK cost free. It is an opensourced framework.
http://osflash.org/projects has a list of opensource tools available to create flash content.