The Final Hours of Portal 2 Teaser Website mentioned last night now reveals this is for The Final Hours of Portal 2 for iPad on the iTunes App Store, as Geoff Keighley has created an app based on his "unprecedented 'fly on the wall' access [to Valve] over the past three years to create this staggering 15,000 word multimedia experience." The intro also mentions a "hush-hush Portal prequel that was shelved," and looking to get the most of their $1.99, Kotaku shares details about this, saying that for five months in 2008 Valve was developing a Portal prequel set in the 1950s which did not actually include Portals. They say this was based on a new "F-Stop" gameplay mechanic that Valve was very excited about, but apparently play testers had a different vision for a Portal follow up, wanting it to include Chell, GLaDOS, and yes, portals. It seems this F-Stop gameplay mechanic will still show up in a future game, as Valve is keeping it under wraps, though Keighley's app includes F-Stop concept art that keeps its secrets safe. Also included is word on a Half-Life reference that was cut from Portal 2 and details on game prototypes Valve worked on during a three-month period when they took a break from other scheduled projects.