Take a look at F-Stop, the Portal sequel you'll never play
Portal 2: F-STOP PROJECT CAPTURE - Full Walkthrough - YouTube
Valve possibly working on third portal game, But But it is not portal 3 : r/Portal
Over a decade later, we have a snapshot of Valve's cancelled Portal sequel, F-Stop | Eurogamer.net
Valve Archive no Twitter: "Portal/Portal 2/Art/F-STOP; Old Aperture/testchamb1.jpg Found in folder: https://t.co/05Gj6Ky8sH https://t.co/1Umk29H9eE" / Twitter
Valve'ın Kayıp Projesi F-Stop, Bir Videoda Ortaya Çıktı - Webtekno
Portal's abandoned prequel, 'F-Stop,' surfaces in a new video authorized by Valve - Polygon
Portal could have had a prequel called F-STOP/Aperture Camera, as a new documentary shows | GamingOnLinux