https://www.polygon.com/2017/11/23/16694876/sanctum-2-is-free-on-humble-bundle

Humble Bundle is offering Windows PC shooter Sanctum 2 for free, at least until the end of the week.

The game, developed by Coffee Stain Studios, is usually priced at $14.99 on Humble Bundle. Released in 2013 to mostly good reviews, it's a mixture of tower-defense and first person shooter.