While the cake may be a lie, the fact that Valve is giving away free copies of Portal is certainly real. From now until September 20, Steam users can download and install either the PC or Mac version of the classic puzzle game.

The most anticipated question is whether or not this is simply a free trial or in fact a 100 percent free game. We are happy to report that the latter is the case. So long as you download and install the title before the 20th, it's free and will remain that way indefinitely.

Portal is being given away to help promote Valve's "Learn with Portals" program, an education-based initiative designed to teach school-aged children about science. The program allows kids to design their own Portal levels, meaning they need to use physics, math, logic, probability and spatial reasoning to succeed. What better way to teach admittedly boring skills than designing a video game? It sounds like a win-win for everyone involved.

If you are unfamiliar with the series, Portal was launched in October 2007 as part of a game bundle called The Orange Box. Portal is a first-person puzzle game that requires the user to use a handheld portal device to open inter-spatial portals between two flat planes. The main character is instructed to complete varying tasks by an artificial intelligence called GLaDOS (Genetic Lifeform and Disk Operating System) with the promise of cake once all tasks are completed.

The sequel, aptly named Portal 2, was released on April 19, 2011 and is currently available on Steam for $29.99.