“While attempting to travel to the future to get a copy of Portal 3. I accidentally traveled to alternate-1987 and obtained a copy of Portal 1 for the Apple II!”, Weaver says.
“In actuality I originally just planned to do the end credits. But the Apple II high-res mode has the perfect Aperture Science orange and blue colors, and one thing led to another… ”
Of course this project is just for fun and is in no way endorsed by Valve, etc.
Check out the Kerbal Space Program port by Vince as well!