MTASC : Motion-Twin ActionScript 2 OpenSource Compiler.
http://team.motion-twin.com/ncannasse/mtasc.html

You can put the "std" directory as a subdirectory of the
dir you installed the mtasc binary, or you can specify each
time you want to compile the classpath to flash class headers
stored into the "std" directory using the -cp commandline
parameter.