zeogold: Note that I generally don't include stuff that required a purchase, only stuff that was straight-up free.
Sure, here you go.
1 AGE OF WONDERS
2 ALAN WAKE'S AMERICAN NIGHTMARE
3 ALIENS VERSUS PREDATOR CLASSIC 2000
4 BATTLE REALMS + WINTER OF THE WOLF
5 BROKEN SWORD: DIRECTOR'S CUT
6 CARMAGEDDON MAX PACK
7 DUKE NUKEM 3D ATOMIC EDITION
8 DUNGEON KEEPER GOLD™
9 EMPIRE EARTH GOLD EDITION
10 FALLOUT 1
11 FALLOUT 2
12 FALLOUT TACTICS
13 GIANTS: CITIZEN KABUTO
14 JAGGED ALLIANCE: DEADLY GAMES
15 LITTLE BIG ADVENTURE
16 MAGRUNNER: DARK PULSE
17 MOUNT & BLADE
18 OMERTA: CITY OF GANGSTERS (4 DLCS INCLUDED)
19 REALMS OF ARKANIA 1+2
20 REALMS OF ARKANIA 3
21 RISE OF THE TRIAD (2013)
22 STILL LIFE 2
23 THE DARK EYE: CHAINS OF SATINAV
24 TORCHLIGHT
25 WITCHER 2: ASSASSINS OF KINGS, THE
26 WORMS: FORTS UNDER SIEGE
27 CONSORTIUM: MASTER EDITION
28 SYSTEM SHOCK 2
29 LITTLE BIG ADVENTURE 2 (TWINSEN'S ODYSSEY)
30 NEVERWINTER NIGHTS: DIAMOND EDITION
31 CONSTRUCTOR
32 SAINTS ROW 2
33 FANTASY GENERAL
34 EADOR: GENESIS
35 JOTUN: VALHALLA EDITION
36 DEADLIGHT: DIRECTOR'S CUT
37 ODDWORLD: ABE'S ODDYSEE
38 STRONGHOLD HD
39 A.D. 2044
40 SYBERIA
41 MDK
42 GRIM FANDANGO REMASTERED
43 OXENFREE
44 CARMAGEDDON TDR 2000
45 KING OF FIGHTERS 2002
46 DUNGEONS II
47 UNREAL GOLD
48 XENONAUTS
49 ZIGGURAT
50 SHADOW WARRIOR 2
51 FULL THROTTLE REMASTERED
52 SOMA
53 DISTRAINT: DELUXE EDITION
credit:
https://www.gog.com/forum/general/list_of_free_games_on_gog/post5 edit: adding credit.
edit2: adding Distraint, which I missed.