There have been a few Portal fan-films, but the latest – Portal: Survive – is definitely one of the best realised and well made.
The short film was made by Colin and Connor McGuire, and only cost around $500 to make.
The film even features a real life GLaDOS prop which was created by Angry Dog Studios.
You get to see the origins of GLaDOS in the Aperture Science labs, and of course, her insane trials that she puts Chell through.
Check it out below: