Notably, forms became instantiable objects, thus laying the foundational concepts of class modules as were later offered in VB4. "As" here means essentially: "Notably, forms became instantiable objects, thus laying the foundational concepts of class modules like those that were later offered in VB4."

as = like; the same as

It's kinda like "at the same time" or "also" in the context. By any chance, are you a programmer?