I forgot about Mount and Blade Warband too - I have it on Steam and GOG.

The Longest Journey - Boxed and GOG
Battlefront 2 - CD and GOG
KotOR 1 - A boxed and a CD version (one that came with 1+2 a year-ish ago
Cave Story+ - I got a version from Steam, and then from Humble Bundle simply for the DRM-free version.
C&C - CD and Origin
C&C Red Alert - CD and Origin
C&C Tiberian Sun - CD and Origin
HoMM 4 - GOG and CD+1 expansion
Half Life 2 - Boxed and Steam
Total Annihilation - CD and GOG
Sims 2 - CD and Origin

I have purchased quite a few games more than once due to sales, either to replace a physical copy or just because with digital services you never know -- someday a site could go out of business and boom, you lose any games you didn't back up. Sure, the business would probably come out of bankruptcu with a new owner, but there's no guarantee you wouldn't lose stuff you had paid for.

I have multiple copies of only a few games:

Baldur's Gate II (boxed and GOG)
Freedom Force (boxed and digital from GamersGate)
Neverwinter Nights (the boxed original, each of the boxed expansions, the Diamond edition, and GOG)

Many copies of the older C&C games by westwood both physically and digitally as well as three sperate copies of freespace 2 basically because i can play them all till the day i die.

Most of the games I have purchased on GOG were to get digital backups of older games that I already owned. In other words, the "Good Old Games" games. There are exceptions, but I counted 27 such in my account. I've also done this for a fair number of games that don't exist on GOG including Sid Meier's Pirates!, Sid Meier's Railroads, Civilization 3/4, Galactic Civilizations 2, Morrowind, Oblivion, and Titan Quest.

You're 100% loyal to that great game. :)

Terraria comes in mind. Just to support the developer.

And probably games I bought on Steam I bought here as well. Now I buy most games here and rarely on Steam anymore. 219 and counting... :-)

Do you mean on the same platform? Because I bought KOTOR on both PC and Android, same for Syberia and Broken Sword 1/2 (and maybe others I don't remember).

On PC, I don't remember many. I remember I bought Giana Sisters on Steam with the plan of buying it DRM-free when it appeared on a $1 bundle, and then I bought the Humble Bundle for it. There are other cases, but it's usually when the bundle contained other stuff I wanted, and getting another version of a game I owned was only a bonus (or just something that happened).

Thinking about it a bit more, I think I have Broken Sword 1,2 on CD too, but since Director's Cut is different, I don't know if that really counts. If it is, maybe Monkey Island Special Edition counts too?

vampire bloodlines ?
yes

Baldur Gate.

Maybe 4 physical copies, one copy each on GOG, Steam, GamersGate, Impulse / Gamestop, then the EE edition on GOG again so together 9 copies?

Around 30 games...


Retail boxes / GOG:

▪ 11th Hour
▪ 7th Guest
▪ Beyond Good and Evil
▪ Bioforge
▪ Broken Sword
▪ Broken Sword: The Sleeping Dragon
▪ Duke Nukem 3D
▪ Gabriel Knight 2: The Beast Within
▪ Ghost Master (2 retail boxes)
▪ Little Big Adventure
▪ Phantasmagoria
▪ Phantasmagoria 2: A Puzzle of Flesh
▪ Realm of the Haunting
▪ Return to Zork
▪ Sam and Max Save the World
▪ Shogo
▪ The Last Express
▪ The Longest Journey
▪ The Pandora Directive
▪ Under a Killing Moon
▪ Zork Nemesis


Retail boxes / Gamersgate:

▪ Death to Spies
▪ Death to Spies: Moment of Truth
▪ Evil Genius
▪ Far Cry
▪ Mafia: The City of Lost Heaven
▪ Tomb Raider: Anniversary
▪ Tomb Raider: Legend
▪ Tomb Raider: Underworld


Retail boxes / Steam:

▪ Sid Meier's Pirates! (2004)

...

The game that I have bought the most copies is Civ3. The game wasn't released in Taiwan until the Complete Edition came out. Being an addict that I am, I purchased the limited tin-boxed collector's edition from Amazon when it came out. The shipping costs almost as much the game itself. I bought the Complete Edition in Taiwan to get the expansions later. I got the Complete Edition again when I bought Civilization Chronicles for Civ4. And finally, I also bought a copy for Steam when I bought Civ5.

The titles in this LucasArts release. I still have a ton of old LucasArts games on disk, but most of them don't work any more... because the disks are scratched, I've lost the serial keys, or because they're just outdated and won't work on my Windows 7 system. So grabbing these on GOG is a second chance for me to back these games up, not mention actually get to play them again.

I will just do a small number of games I either bought multiple physical copies of, or re-bought as Digital Downloads. The number I have through bundle overlaps is ridiculous.

Broken Sword 1-4 /\ Diablo 2 /\ GTA - SA /\ Dawn of War 1 - Soulstorm /\ Lemmings /\ Monkey Island 1-2 + TellTails (+ 1 remastered edition) /\ Sam and Max /\ Killswitch /\ Sacred 1-2 /\ Temple of Elemental Evil /\ Time Commando /\ Hitman 1-4 /\ Resident Evil 2 /\ Zelda 1 & Majoras Mask /\ Quake 2 /\ Fallout 3 /\ Halo /\ Doom 3 /\ All but 2 of the Apogee games on GOG /\ Balders Gate 1-2 + EE's /\ The Witcher /\ Binding of Issac /\ Theme Hospital /\ Stalker 1-3 /\ Deus Ex 1-2 /\ Project Eden /\ Unreal 2 + 2004 /\ Shogo /\ All Tomb Raiders here + Anniversary /\ Demon Stone /\ Nox /\ Simon the Sorcerer 1-2 /\ Neverwinter Nights /\ MDK /\ The Book of Unwritten Tails /\ Theif 1-2 /\ Incomming /\ Duke Nukem 1 + 3D /\ Z
, and many more I just cannot think of right now, and every Pokémon remake too. Games have eaten up a lot of my money over the years. That and my music collection.