Portal is designed to change the way players approach, manipulate, and surmise the possibilities in a given environment; similar to how Half-Life 2’s Gravity Gun innovated new ways to leverage an object in any given situation.

Players must solve physical puzzles and challenges by opening portals to maneuvering objects, and themselves, through space.

With the official launch of Steam for the Mac, Valve wanted to celebrate its accomplishment. Since it couldn’t share cake with the world, the company decided to offer totally free copies of Portal to any and all customers.

To get in on the fun you just need to install the Steam client for PC or Mac, then hit the Steam store and “purchase” Portal for the grand total of $0.00. Don’t delay though, as this offer is only good until May 24th.