Made by Gearbox Software and originally released in 2001 as an add-on to Half-Life, Blue Shift is a return to the Black Mesa Research Facility in which you play as Barney Calhoun, the security guard sidekick who helped Gordon out of so many sticky situations.
A very short but fun game good to see Blackmesa through the eyes of someone other than Gordon Freeman lacks a bit of content but all in all a very fun game.