SCASM is a scenery compiler created by Manfred Moldenhauer. SCASM is an abbreviation of SCenery ASseMbler. SCASM is a tool which history goes back till Flight Simulation 5.0. Until FS2002 SCASM has been updated by adding the new elements from the SDKs.
Since the release of GMax with FS2002 there has been talk about SCASM based scenery being bad. This is not the case, as long as the commands from the FS2002 SDK are used. It is then possible to create binary similar scenery with either SCASM or GMax and the FS2002 gamepack. But SCASM can not make the MDL style scenery objects that have been introduced since FS2004. Backwards compatibility of Flight Simulator still allows the display of SCASM generated BGL files though.