StarCraft Anthology (PC/Mac) – FREE
Play through a storyline that spans 58 missions spread across six campaigns, creating a true sci-fi epic. Follow Jim Raynor on his quest to save the Terran colonies from destruction; serve the cunning Zerg Overmind as it hatches a deadly plan; and lead the Protoss Prelates in the desperate defense of their homeworld.
The game is now permanently free with the latest patch. More info here.