JPEXS Free Flash Decompiler is an open source tool for decompiling Flash SWF files, extracting, editing or replacing their contents.
At a minimum you might use the program to grab images, videos or music from an SWF.
You could also tweak an applet, perhaps replacing a background image or the soundtrack. Flash developers might explore scripts to better understand how an applet works, or security experts can analyse a malicious applet to figure out what it's doing.
Whatever you're doing, the program is reasonably easy to use. There's no installation, and it's Java-based, so works almost anywhere: just open your applet and its various resources are displayed in a tree: shapes, sprites, buttons, fonts, frames, scripts and more. Expand a section like Sounds, then browse their contents, and right-click an item to view, remove, replace, export it and more.
JPEXS Free Flash Decompiler has plenty of other higher level functions. If you can't find an SWF file, it's able to search your browser cache, or even its RAM. And whatever you locate may be exported as a stand-alone EXE file, for easy playing on the Windows desktop.
Version 9.0 brings (Changelog):
JPEXS Free Flash Decompiler is a powerful application with a stack of essential features, yet remains accessible - and very useable - to non-developers.