Black Mesa (previously known as Black Mesa: Source) is a third-party total conversion modification for Valve Corporation's Source engine. The stated goal of the project is to recreate Valve's critically acclaimed 1998 video game Half-Life
using the more advanced capabilities of the Source engine. The
40-person volunteer development team says they hope to create a more
engrossing in-game world with more varied, complex environments and more
challenging, realistic gameplay.

During its eight years in development, Black Mesa has been
featured in several video game publications and received direct
attention from Valve. Due to its long development time the modification
became notable for its delays, and dwindling updates on the status of
its completion. The delays led to Wired awarding Black Mesa high spots on their "Vaporware Of The Year" lists in 2009 and 2010.en.wikipedia.org/wiki/Black_Me…video_game%29#cite_note-2en.wikipedia.org/wiki/Black_Me…video_game%29#cite_note-3

The first part of Black Mesa, featuring remakes of all Half-Life's chapters except those set on the alien world "Xen", was released as a standalone download on September 14, 2012.en.wikipedia.org/wiki/Black_Me…#cite_note-kotaku091412-4en.wikipedia.org/wiki/Black_Me…video_game%29#cite_note-5 Public voting through Valve's Greenlight program saw the game approved for distribution on Steam.

Its out now you can download it here: release.blackmesasource.com/
And its completly free en.wikipedia.org/wiki/Black_Me…te_note-steamgreenlight-6en.wikipedia.org/wiki/Black_Me…video_game%29#cite_note-7en.wikipedia.org/wiki/Black_Me…video_game%29#cite_note-8