There aren't many studios that can rival Valve's capacity to keep the lid on a yet-to-be-released project and the latest news once again confirms this, as it took an indie dev LunchHouse Software to show us F-Stop, Portal's unreleased prequel.
"Exposure is a project in development by us at LunchHouse Software, taking the form of a multi-part video series which documents the mechanics of Valve's F-STOP. The mechanics are not based on speculation or hearsay. Instead, Exposure uses the original, official code from Valve's own F-STOP, or as it was properly named, Aperture Camera" the description reads.
F-Stop's story is quite a long one, as it was initially a project unrelated to Portal. The name F-Stop is not coincidental and if you're dealing with photography, you'll know why Valve chose to refer to the game as they did then. Not that we were part of the process, mind you.
As you can see from the video, F-Stop players were tasked with finding their way out of various rooms, which is very Portal-like, but where it really stands out is how you go about it. Unlike in Portal, there are no portal-guns to get you out of a tight spot - it's all about using the camera to capture items and then magically make them a reality.
Eventually, the game was planned as a Portal sequel, more-precisely a prequel, and while it certainly had some merit to inherit the franchise's branding, Valve thought otherwise. F-Stop was eventually dropped by Valve and Portal got its proper successor in 2011 with Portal 2.
Note that even though the mechanics you see may not seem all that impressive today, especially if you played Superliminal, one decade ago it was quite impressive. Even describing F-Stop would've been difficult, and you'd have to reach for Fatal Frame meets Portal comparisons, while still being off-target.