I just looked up the game which I have the most versions of.

And the winner is... Defender of the Crown. My "Extended Collector's Edition" (limited to 500 units) contains the following versions

• Amiga CDTV version (CD-ROM)
• Amiga CD32 version (CD-ROM)
• legal emulation of the classic Amiga version
• legal emulation of the extended Amiga version
• legal emulation of the Amiga CDTV version
• legal emulation of the Amiga CD32 version
• legal emulation of the CD-i version
• legal emulation of the C64 version
• legal emulation of the Apple II GS version
• legal emulation of the Amstrad CPC version
  
• legal emulation of the ZX Spectrum version
• legal emulation of the DOS version
• legal emulation of the Mac version
• legal emulation of the Atari ST version
• legal emulation of the NES version

I also have the Android version based on the Amiga version.

Okay, that was a bit of cheating cause I bought all of the above (except the Android app) as one product.

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Oh, I bought 8 versions of the point&click adventure "Machinarium" in that order:

• Steam version in 2009
• then I got it in a Humble bundle
• PS3 version (flash sale)
• GOG version (Collector's Edition)
• iPad version
• Vita version
• Windows Store
• Android

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Day of the Tentacle:

• retail CD-ROM (English version)
• retail CD-ROM (German version)
• DotT Remastered (PS4 / Vita Cross-buy)
• DotT Remastered (Steam)
• DotT Remastered (iOS)
• DotT Remastered (GOG)
• DotT Remastered (Twitch)

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Grim Fandango:

• retail CD-ROM (English version)
• retail CD-ROM (German version)
• GF Remastered (PS4 / Vita Cross-buy)
• GF Remastered (Steam)
• GF Remastered (GOG)
• GF Remastered (iOS)
• GF Remastered (Android)

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Limbo:

• Steam version
• GOG version
• PS3/PS4/Vita cross-buy
• Xbox One version

Oh man all the time. I’ve gotten the HD versions of ratchet and clank 1-4, GoW 1-3, shadow of the colossus (twice since I just got the ps4 version, TWD season 1, MGS3, crash trilogy, GTA5, Arkham games, uncharted trilogy, last of us, sleeping dogs, will get Spyro trilogy, and several others after owning them in original form already. I love re-living my favorite games on a modern console with some updates and getting those sweet sweet trophies.

Why would you even do this? I’m completely baffled as to why anyone would buy the same game twice. The only reason I can’t see would make this seem reasonable would be if you had a physical copy and lost it or broke the disc and need it to still play the game. Otherwise a complete waste of money.

I don't do it too often, but I have a few cases, such as Puyo Tetris (both English and Japanese) and soon Death Road to Canada (PC and Switch). I'm usually fine just having the one game unless the original copy I have is really old and wearing out.