Portal: Prelude is an unofficial prequel to the game Portal, developed by an independent team of three. The game features a brand new storyline focusing on the pre-GLaDOS era of Aperture Science where test subjects are monitored by employees of the facility. The game spans across 8 chapters covering 19 test chambers which follow a gradual learning curve similar to that of Portal. In addition, 48 challenge maps and 6 advanced test chambers are included with the mod.
Many gameplay elements from Portal make a return in Prelude, while entirely new gameplay devices were created exclusively for the mod, such as localised gravitational fields. Portal: Prelude also features over 400 lines of voice acting, with English, French and German subtitles.
Shortly thereafter, the player receives a Handheld Portal Device. However, this Portal Gun is not fully upgraded, and, unlike in Portal and Portal 2, can only shoot orange portals. After the player proceeds through a number of tests, he or she receives a Dual Portal Device. The player proceeds through more test chambers, encountering new people and gameplay mechanics, such as Peter and Localised Gravitational Fields. The Weighted Companion Cube also makes an appearance, though like in Portal the player must euthanize it at the end of the chamber. After the player completes the final chamber, they return their device and proceed to their party. However, the party must be delayed because of the activation of GLaDOS. The player gets to watch the activation of GLaDOS. However, its Morality Core was not installed, and so she kills most of the employees in the room. Mike shuts the whole system down, but the auxiliary power will turn on in a few minutes, so the player must quickly find the morality core and install it on GLaDOS.The player finds a new Portal Gun, and proceeds to find the Morality Core. However, by the time they get back to GLaDOS's room, she has already awoken and has started filling the facility with a deadly Neurotoxin. After evading GLaDOS's traps, the player finally manages to install the Morality Core. However, their effort is in vain, and the deadly Neurotoxin supposedly kills the player.
- Portal: Prelude won third place in ModDB's Mod of the Year 2008.
Though other female characters are mentioned, all of the employees the player sees in the mod are men and have nearly the exact same design, excluding the party hats near the end of the game.
- Portal: Prelude homepage
- Portal: Prelude on the
- Portal: Prelude 2013 hotfix/patch (1.1.5), for getting the mod to work post-SteamPipe update