Merlin was red and looked kind of like an early cell phone, not that we knew that back then. By modern standards, you couldn't do much with it -- you could play six simple games, against friends or the computer. (One, Echo, was a lot like Simon, actually.)
Merlin was the best-selling game of 1980. I never had one, but I know at least one of my friends or cousins did. It was pretty cool, and seeing kids walking around holding it and playing it (you really couldn't WALK with Simon) was like a precursor of today's kids and their handheld games and smart phones of all kinds. Today it looks enormous and simplistic, but back then it was a treasure indeed.
Did you have Merlin? Did a friend? What early computer substitutes were your favorites?