The developers behind the painstakingly created remake of the original Half-life got approval from Valve to sell a standalone version of the mod on Steam. Black Mesa was one of the first titles approved by fans on Steam Greenlight. Originally created “just because” and released for free Black Mesa is a perfect recreation that elevates the original classic to the more modern Source engine.
It speaks volumes of the quality of this mod and the developers behind it that Valve is allowing their intellectual property to be licensed and sold on their own distribution platform.