Portal: Prelude

Portal: Prelude is a mod for Portal which aims to extend the Portal storyline.

Story
The story revolves around the pre-GLaDOS epoch, even before she was plugged in. At this time, test subjects were monitored by real Aperture Science employees, whose work was tedious, lengthy and repetitive. This is why they decided to build a great artificial intelligence that could both replace them in these difficult tasks, and also take responsibility for many other tasks within the complex and compete with Black Mesa's superiority. All employees of the Aperture Science complex are now eagerly awaiting GLaDOS. Maybe even a little too eagerly, as the upcoming events will tell.

Features
Portal: Prelude is a whole new story where the player takes the role of Abby, a test subject (whose model mostly consists in a blond Chell model with other changes), monitored by Aperture scientists with British accents who tend to make humorous comments. The game offers a few more gameplay hours than the original Portal, with 8 chapters, 19 test chambers, 48 challenges, 6 advanced maps, a brand new storyline and more than 400 lines of speech with various languages (as subtitles).