The popular game, Portal, has been made available via a free download for a limited time (May 24). Since I have never personally played it, I am getting the description of the game from Wikipedia's page:

The game consists primarily of a series of puzzles that must be solved by teleporting the player's character and simple objects using the Aperture Science Handheld Portal Device (ASHPD, also dubbed the portal gun), a unit that can create inter-spatial portals between flat planes. The player character is challenged by an AI named GLaDOS to complete each puzzle in the Aperture Science Computer-Aided Enrichment Center using the portal gun with the promise of receiving cake when all the puzzles are completed. The unusual physics allowed by the portal gun are the emphasis of this game and are an extension of a similar portal concept in Narbacular Drop;

Again, I have not personally played this game, but it seemed like something our readers might be interested in taking advantage of. Portal is available for both Windows and Mac users so if you are looking for a unique first person puzzle game, give it a try as you have nothing to lose.