Steam link: https://store.steampowered.com/app/620/
Short Description: The "Perpetual Testing Initiative" has been expanded to allow you to design co-op puzzles for you and your friends!
Platforms: Windows Mac Linux
Publisher: Valve
Developer: Valve
Release: Apr 18, 2011 (13 years, 7 months ago)
Price: $9.99
Reviews: 344,463
Score: 10/10
Followers: N/A
Tags: 3D Platformer Action Action-Adventure Adventure Atmospheric Comedy Co-op Dark Humor Female Protagonist First-Person FPS Funny Level Editor Physics Platformer Puzzle Puzzle Platformer Science Sci-fi Story Rich
Genres: Action, Adventure
Revenue Estimate: ~$66 million