Portal may be the name for a contemporary series from Valve, about mad robots and jumpsuits, but it's also the name of a video game first released nearly thirty years ago.
That game, Portal - Valve got the trademark after the original ceased using it - was a strange adventure title for personal computers, and was published by, of all companies, Activision.
Portal's story is a great one: you're an astronaut who, after spending 100 years in space on a mission, returns to Earth to find everyone gone and the planet an overgrown wasteland. Picture Life After People, only in a text-based adventure game.
Your goal, then, is to talk to a computer system called Homer, and by going back through its records try and piece together what happened. And that's it! No killing, no jumping, you were essentially digging your way backwards through a very depressing story. Think of it as Dear Esther 1986, if you will, complete with the very valid point that it was only half a game, the other half being some kind of interactive story.