General purpose preprocessor is much like C preprocessor but independent of file type. GPP is not actively maintained, but it works. Its home page hosts binaries for various *nix systems, but no windows build. Few years back I’ve found windows build at wichers.nu, but this link is dead now, and it looks like GPP windows build is not available anywhere else. So to fix this problem,
I uploaded GPP windows build copy to google code, where it will now reside for the rest of its days. Update: google code is gone, so I reuploaded GPP windows build to GitHub now.
Obvious applications for windows-based flash developers include easy code obfuscation or inlining (with no garbage left in your swf), or you may try and be creative :)