Doom: Mac + PC (DOS) + Doom's Collector (Windows) + ID Anthology + SNES + 3DO + Jaguar. So I bought Doom 7 times.
For The Witcher it's weird but I bought it 3 times but don't know why. The first was the collector edition released in my country with initial international release, the second the SE. But in between I also get another cheap collector edition and don't remember why!