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Dragon's Dogma Dark Arisen

Have yet to buy it on GOG, but that will happen sooner-than-later
It's 9 bucks for a few more hours.
Neverwinters Nights
Elder scrolls Morrowind & Oblivion
Fallout 1,2 tactics, 3 and New Vegas
Star wars empire at war.

For me i bought Morrowind 5 times 4 on disk, 1 on steam and then on gog i loved the game so much.
Forgot to add Mafia II (3x)
I bought three super-duper copies of Neverwinter Nights 2 on release, but I still haven't played it much past the tutorial, though I do still own a DVD version. I will, no doubt, eventually buy it from Gog.

I first found Gog when I was looking to play my CD copies of Fallout and Fallout 2, so I bought them.

I also bought Dragon Age: Origins from a store about ten years ago but couldn't play it on my old laptop, then my new laptop didn't have an optical drive so I couldn't install it (as for NwN2), so it was only last month when I finally got to play it, after purchasing it a second time from Gog.

There are probably a few others, but most of the rest of my library consists of games I had not purchased before.
I just bought Blackguards II for the PS4... after buying 1 & 2 here on GOG.