The software is not the full game but contains core information about it.
Developers Valve have confirmed that the software that has appeared on the net is indeed the computer code behind the game.
It includes the physics engine, the sound system and various other pieces of code from other developers, but not any of the levels or the graphics.
Half-Life 2 (PC)
Once again players assume the role of Gordon Freeman, a scientist destined to save the Earth from hordes of gruesome alien attackers. Half-Life 2 takes computer games to a new level of realism with incredible in-game graphics that recreate familiar-looking city streets, and blend them with strange and grotesque monsters, resulting in a believable and at times unsettling environment. Objects and characters feature accurate physics properties, behaving with the appropriate mass, density, and physical properties of their real-life counterparts. Extremely intelligent computer AI result in enemies that plan, adapt, and respond to the player’s actions. 
Buy this game:
http://gamespy.pricegrabber.com/user_sales_getprod.php?masterid=1410545&lot_id=2424373
(Half-Life 2) Download Source code:
32 MB
Uploader: 
(Half-Life) source code from file planet (Free):
Enjoy! 
thank a lot
your site have big power by you
dont have program for creat comic strip?
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English please. There is no translator
valeu cara, thank you guy, i have search for this sdk for a long, long time but your site help -me. god bye thanks!
thanks man, thanks man I have tried this sdk for long, long time but thanks to your website I found, bye thanks man!
Deal all, how can i use this…. i want to make a level… i need some tips…. plz help me