Blizzard announced that StarCraft 2 was going to be free-to-play starting on November 14th. For those who owned the game before October 31st, Blizzard is automatically giving you Heart of the Swarm for free as long as you login to Battle.net between November 8th and December 8th 2017. The game is 7 years old, but it is still a terrific game and well worth trying. The StarCraft II version comes with the original Wings of Liberty campaign with the Heart of The Swarm, Legacy of the Void, and Nova Covert Ops campaigns available for $14.
Source: https://www.bleepingcomputer.com/news/security/blizzard-makes-starcraft-2-free-to-play-learn-how-to-get-it/