On the off chance that you don’t already own Valve’s original Portal title, for a limited time you can scoop it up on the free. Between now and September 20th, if you download the game on Steam, you’ll get to not only play the game, but keep it forever.
The promotion is part of Valve’s “Learning With Portals” program, where the company promotes Portal as a learning tool for aspiring young developers. On Steam, the game comes with free authoring tools which you can use to create your own creations.
Promotion runs from now until September 20th.