3IXAM Software stole the Blender Source Code to sell it as an "Original" product. The screenshots show the IDENTICAL file structure. More in Comments. : r/blender
Steam Community :: Guide :: Practically any model to SFM via Blender 2.7x (The Hard Way) Course
Mesh Source - Blender Market
Blender tutorial - Valve Developer Community
TUTORIAL] Blender and the Source Engine | TF2Maps.net