Notice: This fork is used in the mtasc-install project. Please refer to that project for documentation. Don't expect any big changes from my end, though; I'm just happy it compiles. In that spirit, forking is encouraged ;)
MTASC stands for MotionTwin ActionScript Compiler.
It was an open source AS2 compiler which Nicolas Cannasse wrote at MotionTwin back in time, and somehow the grandfather of Haxe.