A trial version app for Mac, by Valve.

The new Half-Life 2 is a continuation of the story from the first game. You play as scientist-author Gordon Freeman, who is on a mission to save the world from the danger he created in the first game.

You start in an alien-infested world and looking for any remnants of civilization. Your mission is to find people left alive to learn what happened to the rest of the world and find out what is going on in the mysterious, empty buildings. You will need to collect tools and weapons to help you.