Portal

Portal is a first-person puzzle game developed by Valve Corporation and released in late 2007. In the game, the player controls a female test subject named Chell in the Aperture Science Enrichment Centre. Guided by a female electronic voice-over of a supercomputer named GLaDOS, the player uses the Aperture Science Handheld Portal Device ("portal gun") to perform a variety of tests, such as creating portals to knock over turrets and other objects or moving to a previously unreachable area, so that they may advance to the next test.

Portal is set in the Half-Life universe, and although there are no direct references to it in the game, there are many similarities between equipment in Portal and in Half-Life 2; turrets, for example, are quite similar in both games, and Portal also uses energy orbs identical to those in Half-Life 2. The backstory to Portal is explained in Half-Life 2: Episode Two, although the story behind Chell is explained throughout Portal.

Portal is the sequel to Narbacular Drop, a freeware game released by students of the DigiPen Institute of Technology.