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.
This pack does not just include maps that I have had archived on my hard drive from the past 20 years. I also ported some maps to Opposing Force. Read documentation for more info. I have made a Windows version of this. The Windows version has utilities for modding Half-Life.