Portal is Valve Software's first commercial singleplayer puzzlegame for PC, Xbox 360 and PS3. It is available on Steam and retail on its own or part of Valve 'Orange Box' package.

Portal is developed by a new batch of Valve employees, Digipen graduates led by Kim Swift who made an innovative puzzle game called Narbacular Drop as their final project. Portal takes the ideas and gameplay of Narbacular Drop and expands upon it - a spiritual successor of sorts. It's been confirmed by Valve that it takes place in the Half-Life universe, but beyond that, details concerning the storyline are largely unknown in relation to the HL saga.

Portal places you in the shoes of a test subject for the company Aperture Laboratories, tasked with testing an experimental weapon called the "Aperture Science Handheld Portal Device," or ASHPD (prompting a plethora of rumours that "Opposing Force" protagonist Adrian Shepard is involved). This gun creates portals on any surface, an ability the player must use to get to the end of the level, avoiding obstacles such as machinegun turrets. The ASHPD is also capable of gravity gun-esque physics manipulation, so that you can pick up objects and throw them through the aforementioned portals. The game presents myriad interesting puzzle opportunities, given that any horizontal or vertical plane can be used to create a portal, resulting in somewhat mind-bending possibilities.

The game is three to four hours long, which is not shabby given the fact that it's a simple puzzle game.