Thanks to the new "Learn With Portals" initiative, which encourages schools to use Portal to teach physics, math and engineering to students, the game is now available for free to both Mac and PC users alike.
The download can be all yours via the above link*, and will remain free until September 20. Has anyone here somehow held off on playing Portal? If that's the case, your weekend assignment is to do so (it only takes about 3 hours) and report back here!
Via MTV Multiplayer
* Or you can just go directly to Steam for the download