Vince Weaver is reimplementing Portal — "the cake acquisition simulator released in 2007" — to the Apple II series of computers, bit by bit — inspired by the fact that the Apple II hires mode has "the perfect Aperture Science orange and blue colors." He's released a disc image of the game in Apple Basic, as well as sourcecode.
Where did you get your time machine?
Well I traded this crazy looking guy some plutonium…
No, really, I just like blinky LED lights and it's the perfect project if you like that kind of thing. I was vaguely trying to get it all finished for the BTTF2/2015 anniversary and it was mostly working but I had grand plans to put it in my car for a while but that never happened. You can find out more here.
There are plans and mostly enough info to build your own copy if you want. A few people have tried, but I've never heard back on any successes.