Last year, some screenshots came up of concept art within Valve studios that looked nothing like Half Life 3 or any of Valve's properties. Apparently, Valve's making a new open-world space game called Stars of Barathrum.
http://www.gamerevolution.com/news/rumor-valve-working-on-stars-of-barathrum-an-open-world-scifi-game-15499
http://www.facepunch.com/showthread.php?t=1217651
http://gamingbolt.com/stars-of-barathrum-open-world-space-game-from-valve-concept-art-leak
http://www.gamerevolution.com/news/rumor-valve-working-on-stars-of-barathrum-an-open-world-scifi-game-15499
http://www.facepunch.com/showthread.php?t=1217651
http://gamingbolt.com/stars-of-barathrum-open-world-space-game-from-valve-concept-art-leak