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 the protagonist is explained throughout Portal.

Portal is the sequel to Narbacular Drop, a freeware game released by students of the DigiPen Institute of Technology, and also ties in with the Half-Life series through Half-Life 2: Episode Two, with a full conclusion expected in Half-Life 2: Episode Three.

Story
You awake as Chell, a woman equipped with implanted heel springs to help her fall from great heights, in the middle of a relaxation room. Immediately the mechanical voice of GLaDOS greets you. It's time to be tested as a human lab rat. Will the experiments go as planned? Just remember: the cake is a lie.