The Source Engine is behind many of the games you love. Just a few include Half-Life 2, Portal, Team Fortress 2, Counter-Strike: Global Offensive and Insurgency. It is also the primary focus of the Wall Worm suite of tools.
Wall Worm has been custom tailored as the one-stop piplene for building assets for Source.
If using Source, make sure that your global settings are set to Source.
Brush Geometry, 3D Skybox, 2D Sky, Animated Textures
Video tutorial and sample file on exporting a 3ds Max scene into a Source VMF file with Wall Worm.