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Portal: The Flash Version is a two dimensional Portal fangame made in Adobe Flash by the studio "We Create Stuff". It features new and re-interpreted mechanics from what the developers could piece together from the Portal trailer.
It seems to take place in it's own universe.
Story[]
The thin story of Portal: The Flash Version has Test Subject 15837 traveling through a testing track using the Aperture Science Handheld Portal Device. They are guided by a voice from above (presumably GLaDOS, though this cannot be confirmed) through the chambers.
At the end of the Testing Track, Test Subject 15837 is given cake, and proceeds through a door into the unknown. What happened to them afterwards is not seen.