100 percent off.
New World Interactive are offering the Microsoft Windows PC version of Insurgency for free until 10:00 AM PDT on August 15, 2018.
While logged into your Steam account, simply click on the "Install Game" button the product page to add the game to your library.
Insurgency normally sells for $9.99. The game won IndieDB's Indie Game of the Year Player's Choice in 2014.