Story:In this challenging puzzle game, you build a computer from scratch and program it. It is a journey through the layers of abstractions of the computer. The game begins when you are abducted by aliens who are testing your intelligence, and from here a lighthearted sci-fi plot evolves.
GOG needs more puzzle/logic/educational games :) this is a good one.
other examples are:
hardchip
SIC-1 (this one is for free on a competing store)
and while I need to fill 160 chars, what about Boltgun Words of Vengeance, which is also free? ;)