F-Stop

F-Stop is a cancelled prequel to Portal, which was made during the Directed Design Experiments. It was approved by Gabe Newell to become "Portal 2" but was scrapped in favor of a direct sequel and more streamlined development.

If you want a quick overview of what F-Stop was, go watch Exposure by LunchHouse Software, who have obtained actual F-Stop code to show off the main mechanic.

To get the full overview of every bit of F-Stop, read through these pages in the order they are in.