I'm not sure if that counts, but I bought many old games here because I sold my physical copies. I wanted to play them again, but boxes took out too much space; besides, all boxes sold were enough to re-buy the digital version.

Monkey Island. I've got pyhsical copies of the first two for the PC, the Xbox and twice for the Amiga; the third for the PC; the fourth for the PC and Play Station; the fifth for the PC. I've bought them all on GOG (one of them might have been free?). I bought that special boxset from limited run games too. All for collection reasons.

Monkey Island 1: floppies, CD, compilation CD with 1 & 2, Special Edition digital download from Telltale, Special Edition DVD and GOG.

Monkey Island 2: compilation CD with 1 & 2, Special Edition DVD and GOG.

Full Throttle: 2 CD versions (EU and Dutch version... I was in Holland for vacations. Friends had ruined my other copy).

Quake: 2 CDs (jewel case and big box) and GOG.

Morrowind, Oblivion, basically any game I had owned on physical formats, I bought on GOG, if they're carrying it. Still waiting for the Discworld trilogy, Flying Corps, Flight Unlimited II, Comanche 3, Civ 2, Daedalus Encounter, etc etc.

Monolith, for a giveaway.
-because it's an amazing roguelite that seems relatively unknown compared to Isaac and Nuclear Throne. Presonally my favorite of the genre, highly polished, actually kinda hard, fun guns and enemies, feels good to play, and there are still updates and dlc comin up.

If i had the space and a console i would probably buy Hollow Knight repeatedly because it's just that good. I would just like to own a physical copy. Similar to Earthbound/Zero/Mother 3 for me.

Kingdom Hearts 1 and 2 (got the originals on PS2. Got them again in the box set along with 3 for PS4 because it was a decent price). These were pretty much the same games on new hardware for easier access (but technically worse since they didnt do a great up scaling from 30 fps to 60 fps and I think they missed some rumble features from the PS2 version).

Witcher 3 (PS4 and PC). Started with PS4 version because I heard good things about the game. Later got the PC version (bought from GOG) due to welcome pack deal and ability to add mods. Didnt get it originally for PC because I didnt have a gaming PC then.

Kingdom Hearts I would consider buying them again on PC at a good sale if DRM-free for better preservation and access to mods (modern TVs need a converter to HDMI for PS2 and who knows if HDMI will be replaced with something else for PS4).

Also Nioh complete edition due to having it on PS4 and the free one given from Epic games.

Nexus: The Jupiter Incident. I've bought it for myself and later on, over the years, several copies for giveaways.

Several games I've rebought to digitize them, such as Creatures, Roller Coaster Tycoon...but in the more literal sense, Age of Empires; I bought twice to get a set with Age of Empires II.

Well, repeat purchases constitute the absolute majority of my GOG library, since I no longer have discs and all.
So I'll list only good games I had more than five physical copies of at the same time: Sacred I and II, Alpha Centauri, original Fallout trilogy, Age of Wonders 2, Tiberian Sun and Red Alert 2, Diablo games, Jade Empire (had an opportunity to grab a box of keepcases cheap to gift people), Heroes III, Cossacks and Vampire the Masquerade Bloodlines.
Legit copies if the first you got wasn't one, great translations, gifts for your friends, improved editions, you get the idea.

Ditto. 3 copies on (original) Xbox (2 of which are GOTY and 1 is the base game) , 1 PC (with both expansions, bought separately) and 1 GoG copy.


Beyond that i bought multiple copies of Ring Runner so i could give copies away, NWN, Disiples, Trine, Baulders gate, and a few others which i was starting my digital collection, and some i got on steam and immediately dropped to do GoG instead.

Many times.

Games I own physically and on GOG:

Unreal Tournament GOTY
Unreal Tournament 2004
Crysis
Inherit the Earth
GRID
Jade Empire
Quake 2
Metal Gear Solid 2

Games I've bought on multiple platforms:

Ghostbusters the Video Game: 360, Epic Store, Switch
Bayonetta: 360, Wii U, Switch
Bayonetta 2: Wii U, Switch
Chrono Trigger: SNES, DS
Dust An Elysian Tail: 360, GOG (16 times if you're counting my giveaways), Switch
Undertale: Humble Store, GOG, Switch
Spec Ops: The Line: 360, GOG
New Super Lucky's Tale: Switch, GOG
Beyond Good & Evil: GameCube, GOG, 360
Axelay: SNES, Wii VC
Star Fox 64: Original on N64, Wii VC, Remake on 3DS
Legend of Zelda: Ocarina of Time: Original on N64, GameCube, Wii VC, Remake on 3DS
King of Fighters XIII: 360, GOG
Batman: Arkham Asylum (both original and GOTY versions): 360, GOG
Batman: Arkham City (both original and GOTY versions): 360, GOG
Deus Ex Human Revolution: Wii U, GOG
Star Wars: The Force Unleashed: 360, GOG
Star Wars: The Force Unleashed 2: Wii, 360, GOG
Rogue Trooper: Original on Wii, GOG, Remaster on GOG
Okami: Wii, Switch
Ori and the Blind Forest: GOG, Switch
Dead Space: 360, GOG
Alan Wake: 360, GOG
Transformers: War for Cybertron: 360, Retail PC
Sonic & Sega All-Stars Racing: 360, Retail PC
Legend of Kay: Wii U, GOG
Darksiders: Original and Remaster on GOG
Dartksiders 2: Original on Wii U and GOG, Remaster on GOG
Sonic Adventure: GameCube, 360
Sonic Adventure 2: GameCube, 360

I enjoyed Mount & Blade warband so much I bought a gog copy later. Bought 3 copies for friends too.

Bioshock Infinite: I bought and played it first on PS3, later I bought it again when I got a 360. I'm waiting for it to go on sale here on GOG. I'll buy it again then with all the DLCs, I've never played those.

Vampire Bloodlines: I bought the rerelease budget jewel case version because it's more convenient to have the game on one DVD instead of several discs but I still keep the old CD-version because the box looks nicer.

Half-Life: I own the German GOTY version as well as the US big box version of the main game and all expansions and I own the game twice on PS2. Again, once the German version, once the uncensored US version.

X-Series: I'm a crazy collector and with the exception of X4 I own every game in the series several times. Regular versions, limited editions, "Gold" box sets, collections and on GOG.

I was curious about that, so I looked through my GOG library and CD/DVD collection.
Here is my list of physical games which I purchased on GOG again:

Anno 1602 + 1503
Aquanox 1+2
Baldur's Gate 1+2
Bioshock 1+2
Deus Ex 1+2 - Invisible War
Divine Divinity 1 + Divinity 2: Dev. Cut
Gothic 1-3
Grandia 2
Icewind Dale 1+2
Heroes of Might and Magic 3 - Complete + 5 - GE
Lands of Lore 1+2
Mafia 1
Might And Magic 6-9
Neverwinter Nights - Diamond
Outcast 1.1
Prince of Persia - The Sands of Time/ - Warrior Within / - The Two Thrones
Realms of Arcania - Blade of Destiny/ - Star Trail/ - Shadows over Riva
Risen 1-3
Sacred 1+2
Spellforce 1+2
Star Wars K.O.T.O.R. 1+2
Sudeki
The Elder Scrolls 3+4
Thief 1+2
Titan Quest
Tom Clancy's Splinter Cell
Tomb Raider 1-3
Two Worlds 1+2
Unreal 1+2
Unreal Tournament + 2004
Venetica

The Time before I discovered GOG, I only played games in physical form. Never liked the conception from Steam and the like. Granted, beside GOG I have also an account on HumbleBundle (bought some DRM-free games there, which were not on GOG) and EGS (for the freebies). That's all.

I've re-bought quite a lot of the games I have on Steam on GOG: Blackguards, Men of War, Spiderweb games (Avernum etc), Divinity, Disciples, No Man's Sky ...My favourites are probably the Men of War games.

I wish I had a digital copy of it, I really liked it and would definetely play it again. I have it on disc for my xbox 360, but a digital verison for PC would have been better.I thought it was unfarily compared to other games instead of being recognized as its own unique thing.This was before amateur reviewers on Youtube overtook the mainstream as the more credible source of opinions, so there was nothing to balance out the close-mindedness of mainstream journalism.