As many of you probably know, Portal is an amazingly popular first-person environment-based puzzle solving game released in 2007. As part of a new campaign called 'Learn With Portals', developer Valve Corporation is giving away the original game for free on the Steam online game store until the 20th of this month to everyone with a Steam account.
Some schools have started using Portals to teach students physics, math, spatial reasoning, logic and other skills. Valve has created a new website about their new campaign to encourage this called LearningWithPortals.com.
Portal is available as a free download for Windows and Mac until 20/9/2011. It is also available in packs (The Orange Box, Portal Bundle and Valve Complete Pack) along with other Valve games for higher prices.
Download Portal for Windows and Mac here.
