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Buy this to get Akalabeth (1998)
Buy this to get Anna's Quest Prologue mini-game
Buy this to get Another World 15th Anniversary Edition
Buy this to get Baldur's Gate 2 Complete
Buy this to get Baldur's Gate: The Original Saga
Buy this to get Beyond Divinity*
Buy this to get Broken Sword: The Shadow of the Templars (Original)
Buy this to get Broken Sword 2: The Smoking Mirror (Original)
Buy this to get Call of Cthulhu: Shadow of the Comet (Floppy Version)
Buy this to get Call of Cthulhu: Prisoner of Ice (UK Version, Windows only)
Buy any of these to get Close Combat
Buy this to get Crimsonland Classic
Buy this to get Crysis Wars
Buy this to get Dark Fall 2 (Original)
Buy this to get Darksiders Legacy Version
Buy this to get Defender's Quest (Original)
Buy this to get Divine Divinity*
Buy this to get Divinity: Original Sin - Enhanced Edition* and previous games* in the series
Buy this to get Divinity: Original Sin Classic
Buy this to get Downfall (Original)
Buy this to get Earth 2140 (DOS Version)
Buy this to get Ether One (Original)
Buy this to get Falcon 4.0 (Windows only)
Buy this to get Hidden & Dangerous Deluxe Edition
Buy this to get Homeworld Classic
Buy this to get Homeworld 2 Classic
Buy this to get Icewind Dale Complete
Buy this to get Jack in the Dark
Buy this to get Karma (short game)
Buy this to get Kentucky Route Zero Interlude [1]
Buy this to get Kingdom (Original)
Buy this to get Lagaf: Les Aventures de Moktar - Vol 1: La Zoubida
Buy this to get Maniac Mansion Enhanced Version (1989)
Buy this to get Master of Orion 1+2*
Buy this to get Master of Orion 3*
Buy this to get Mind: Path to Thalamus (Original)
Buy this to get Oddworld: Stranger's Wrath (Original)
Buy this to get Outcast Classic
Buy this to get Pathologic (Original)
Buy this to get Pid
Buy this to get Postal 2 Complete (Original)
Buy this to get Planescape: Torment (You WILL NOT get another copy if you have owned the game.)
Buy this to get Rad Rodgers: World One
Buy this to get Read Only Memories (Original)
Buy this to get Reprisal (Original)
Buy this to get Retro FPS Prequel Demo (Ion Maiden)
Buy this to get Rocket Ranger (German Amiga Version)
Buy this to get Rune Gold
Buy this to get Seven Kingdoms 2 (Original)
Buy this to get SHENZHEN SOLITAIRE
Buy this to get Shovel Knight: Specter of Torment*
Buy this to get Simon the Sorcerer Legacy Version*
Buy this to get Simon the Sorcerer 2 Legacy Version*
Buy this to get Skaut Kwatermaster (Polish Version)
Buy this to get Sołtys (Polish Version)
Buy this to get Spelunky Classic
Buy this to get Star Wars™ Jedi Knight - Mysteries of the Sith
Buy this to get Stealth Bastard Deluxe Complete Edition*
Buy this to get Strife (DOS Version)
Buy this to get Strike Suite Zero Classic (with all DLCs)
Buy this to get Stronghold Classic
Buy this to get Stronghold Crusader Classic
Buy this to get Stronghold Crusader HD
Buy this to get Sublevel Zero (Original)
Buy this to get System Shock: Classic Edition
Buy this to get Tension (Polish Version)
Buy this to get The 7th Guest (Original Mac Version)
Buy this to get The Bard's Tale (1985)
Buy this to get The Bard's Tale II: The Destiny Knight
Buy this to get The Bard's Tale III: Thief of Fate
Buy this to get The Bard's Tale* (2004)
Buy any of these to get The Elder Scrolls: Arena
Buy any of these to get The Elder Scrolls II: Daggerfall
Buy this to get The Incredible Adventures of Van Helsing
Buy this to get The Incredible Adventures of Van Helsing II
Buy this to get The Incredible Adventures of Van Helsing III
Buy this to get The Mirror Lied
Buy this to get The Raven: Legacy of a Master Thief Classic
Buy this to get The Shivah Classic
Own GWENT and subscribe newsletter to get The Witcher: Enhanced Edition and GWENT Card Keg
Buy this to get Thief (Original)
Buy this to get To the Moon Holiday Special Minisodes 1 & 2
Buy this to get Trine (Original)
Buy this to get Vanishing of Ethan Carter Redux
Buy this to get Vertical Drop Heroes (Original)
Buy this to get Viscera Cleanup Detail: Shadow Warrior
Buy this to get Wasteland* (1988)
Buy this to get Wing Commander 4 (DOS Version)
Buy this to get Wizardry 7 (DOS Version)

* You can buy it directly at GOG
[1] Kentucky Route Zero Interlude: The Entertainment, Limits and Demonstrations,
Here And There Along The Echo

Buy any of these to get The Elder Scrolls: Arena and The Elder Scrolls Chapter II: Daggerfall

Wasteland 2 Standard Edition includes a code for Wasteland 1, and the Deluxe Edition adds another code for The Bard's Tale.

doesnt shadowgate classic come with the new edition ?

The Bard's Tale comes with the classic Bard's Tale trilogy.

Some more , and i know & they are more ...

Akalabeth: World of Doom -> Akalabeth 1998
Call of Cthulhu: Prisoner of Ice -> Call of Cthulhu: Prisoner of Ice - UK version
Call of Cthulhu: Shadow of the Comet > Call of Cthulhu: Shadow of the Comet - Floppy version
Crimsonland -> Crimsonland Classic
Dark Fall 2: Lights Out -> Dark Fall 2 original version
Defender's Quest DX -> Defender's Quest original versionEther One Redux
Ether One Redux -> Ether One Original version
Mind: Path to Thalamus Enhanced Edition -> Mind: Path to Thalamus original version
Oddworld: Stranger's Wrath HD -> Oddworld: Stranger's Wrath original game
Reprisal Universe -> Original Reprisal
The Shivah -> The Shivah classic
Spelunky -> Spelunky classic
Strike Suit Zero: Director's Cut -> Strike Suite Zero classic with all the DLC
To The Moon -> also includes Holiday Special Minisodes 1 & 2

The Incredible Adventures of Van Helsing: Final Cut come with the three games of the original trilogy.
Shadow Warrior (2013) include two different version of the game.
The Original Strife: Veteran Edition include the original Dos version.
The Vanishing of Ethan Carter include the Redux version of the game.
Every Bathesda game will get you a copy of The Elder Scrolls: Arena and The Elder Scrolls Chapter II: Daggerfall.

You can get the original version of Divinity: Original Sin when you buy Divinity Original Sin Enhanced Edition. You have to write a message to support though.

And the original Trine is included when you buy the Enchanted Edition.

Time-limit:
Pre-order Warhammer 40,000: Gladius - Relics of War Deluxe Edition to get Warhammer 40,000: Rites of War

Extra/Bonus key:
Divinity: Original Sin - Enhanced Edition Collector's Edition
Frozen Cortex
Frozen Synapse
Mother Russia Bleeds Dealer Edition

Includes 2 versions:
Bloodnet (CD & Floppy)
Defender of the Crown (DOS & Amiga)
Freddy Pharkas: Frontier Pharmacist (CD & Floppy)
Gobliiins series (CD & Floppy)
Heroes of Might and Magic 2 Gold (DOS & Windows version as game goodie)
Leisure Suit Larry in the Land of the Lounge Lizards (Original & VGA Remake)
Leisure Suit Larry 6 (VGA & SVGA)
Lords of the Realm: Royal Edition (CD & Floppy)
Maniac Mansion (Original & Enhanced)
Police Quest: In Pursuit of the Death Angel (Original & VGA Remake)
Pro Pinball Timeshock (DOS & Windows)
Rocket Ranger (DOS & Amiga)
Shadow Warrior (2013) (DirectX 9 & 11)
Quest for Glory: So You Want to Be a Hero (Original & VGA Remake)
Zak Mckracken and the Alien Mindbenders (FM Towns & Floppy)

Supports original look and feel in remastered version:
Day of the Tentacle Remastered
Full Throttle Remastered
Grim Fandango Remastered (with some exception)
Monkey Island 2 Special Edition
Simon the Sorcerer: 25th Anniversary Edition
Simon the Sorcerer 2: 25th Anniversary Edition
The Secret of Monkey Island: Special Edition
Wonder Boy: The Dragon's Trap

Extracted resources compatible with ScummVM or DOS:
Day of the Tentacle (1993) and Maniac Mansion Enhanced Version (1989) (HOWTO)
Full Throttle (1995) (HOWTO)
Monkey Island 2: LeChuck's Revenge (1991) (HOWTO)
The Secret of Monkey Island (1990) (HOWTO)

Kingdom: New Lands also gives you the original Kingdom game.

The title doesn't really apply to most of those, getting another (often older) edition of a game isn't really a 'bonus game'.

I know, just want to set a good and charming title. :-P

In fact, many gamers love the original Baldur's Gate series and Icewind Dale more.
Enhanced Edition is not better for them.

And, full version of Maniac Mansion is embeded as a mini game in Day of the Tentacle.

Buy System Shock 2 to get:

Corporate Swine
Golf
OverWorld Zero
Street Hog
Swine Hunter
Swinekeeper
Tic-Tac-Triop

(Okay, it's perhaps a stretch, but SS2 does have an in-game "gameboy" <GamePig™> with "cartridges" [if you find them] for the above games, all playable. )

Jack in the Dark is included in the Alone in the Dark trilogy.