Edited:

Things on helpo's list but not mine:
Apotheon
BlazBlue Calamity Trigger
Men of War: Assault Squad
Spycraft: Great Game

Things on my list but not helpo's
Amnesia: Dark Descent
Dracula Trilogy

Of these, Amnesia (173), Dracula (149), Apotheon, and MoW: Assault Squad were all valid guesses. Since I hadn't posted an update noting my oversight of MoW, presumably no one had yet been led astray. ;)

BlazBlue (70) and Spycraft (71) were both put on the board after Rd 1 had closed, but before Rd 2 had opened. So my assumption would be that they were invalid and that both games are still open as guesses for Rd 2. Though as it's phc's game and I'm just a scorekeeper not a referee, phc would be the one to say.

This three were in between the rounds, so they (techincally) weren't guessed yet. But I've already included them in round 2. I'll add [Between the rounds] to them in my lists.

Already had Amnesia (check row 181), but thanks for the Dracula Trilogy.

Hm. I've already promised all my pay to charity, but I'll take a better look at that if necessary.

Full list of guesses up to Rd 3 start:

Limbo guesses (guessed between 1 & 2):
Spycraft: great game
BlazBlue Calamity Trigger

Rounds 1 & 2:
1nsane
7th Guest
7th legion
Act of War: Gold Edition
Afterlife
Agarest: Generations of War Zero.
Age of Wonders: Shadow Magic
Age of Wonders 3
Airline Tycoon Deluxe
ALAN WAKE'S AMERICAN NIGHTMARE
Albedo: Eyes from Outer Space
Alien Shooters
Alone in the Dark
American McGee's Grimm
Amnesia: The Dark Descent
Another World
apache vs havoc
Apotheon
Arcanum: Of Steamworks and Magick Obscura
Arx Fatalis
Assassin's Creed®: Director's Cut.
Avadon: The Black Fortress
Avernum: The Complete Saga
Bad Mojo
Baldur's Gate: Enhanced Edition
Baldur's Gate 2 Complete
BALDUR'S GATE 2 ENHANCED EDITION
Banner saga
Banished.
Bard's Tale
Bastion
Battle Isle Platinum
Battle Worlds Kronos
Betrayal at Krondor
Beyond Good & Evil™
Bioforge
Blackguards Special Edition
Blackwell Bundle
Blake Stone
Blocks that matter
Blood 2
Bloodrayne
Book of Unwritten Tales
Botanicula
Braveland Wizard
Broken Sword 5 The Serpents Curse
Cannon Fodder!
Caribbean
Castles 1+2
Cat Lady, The
Catacombs Pack
Chroma Squad
COGNITION: GAME OF THE YEAR EDITION
Consortium: The Master Edition
Cossacks Anthology
Costume Quest
Crusader: No Regret
Crusader: No Remorse
cultures 1+2
cultures northland + 8th
Cyberia
Daikatana
Dangerous Dave Pack (dupl)
Darkstone
Dead State
Dead Synchronicity: Tomorrow Comes Today
Deadnaut
Death to Spies
Deponia2
Deponia 3: Goodbye Deponia
Depths of Peril
Descent 1+2
descent 3 + mercenary
Descent: Freespace Battle Pack
Deus Ex GOTY
Die By the Sword
Dig®, The
Divine Divinity
Divinity: Original Sin
Doorkickers
Double Dragon Trilogy
Dracula Trilogy
DREAMFALL CHAPTERS SEASON PASS - SPECIAL EDITION
Dreamfall: The Longest Journey
Driftmoon
Duke Nukem: Manhattan Project
D&D Dragonshard
D&D Forgotten Realms: Demon Stone
D&D Temple of elemental evil
Dungeon Keeper 2
Dustforce
Eador
Earth 2140 Trilogy
Earth 2150 Trilogy
Earthworm Jim 1+2
Earthworm Jim 3D
Elminage Gothic
Empire Earth Gold Edition
Empire Earth 2
Empire Earth 3
Eschalon book I
Ether One
Europa Universalis II
Europa Universalis: Rome Gold
Faces of War
Fahrenheit (Indigo Prophecy)
Fall, The
Far Cry
F.E.A.R. Platinum
F.E.A.R. 2: Project Origin + Reborn
Freedom Planet
Freespace 2
Gabriel Knight: Sins of the Fathers
Gabriel Knight 3: Blood of the Sacred, Blood of the Damned
Galactic Assault: Prisoner of Power
Geneforge Saga
Gex
ghost master
Giants: Citizen Kabuto
Gobliiins
Golden Wake, A
Gothic
Gray matter
Grim Fandango
Grim Fandango Remastered
Ground Control Anthology
Guilty Gear X2 #Reload
Gurumin: A Monstrous Adventure
Halfway
Hand of Fate
Hasbro D&D bundle
Hatoful Boyfriend
Hearts of Iron II: Complete
Heroes of Might and Magic IV
Heroes Of Might And Magic 5 Bundle
Hind
Hitman 2
Hotline Miami
ICEWIND DALE: ENHANCED EDITION
ICEWIND DALE 2 COMPLETE
IL-2 Sturmovik™: 1946
Imperialism 2: The Age of Exploration
Incredible Machine Mega Pack
Independence War Deluxe
Indiana Jones and the Emperor's Tomb
Indiana Jones® and the Fate of Atlantis™
Inherit the Earth
inner world
Inquisitor
Ishar Compilation
Jagged Alliance 2
Journeyman Project 1: Pegasus Prime, The
Kentucky Route Zero Season Pass
Kerbal Space Program
King's Bounty - Dark Side
kings quest 7-8
Kingdom Rush
Knights and Merchants
Lands of Lore 1+2
Last Express
Legacy of Kain: Soul Reaver.
Legend of Grimrock 2
Legend of Kyrandia
LEGO: Batman
Leisure Suit Larry Winner (Winner!)
Longest Journey, The (Winner!)
Loom
Lords of the Realm: Royal Edition
Lords of Xulima
Lumino City
Majesty Gold HD
majesty 2 col
Marvelous Miss Take
Massive Assault
massive assault phantom renaissance
Master of Orion 1 + 2 (dupl)
Master of Orion 3
Mdk
mdk 2
Medal of Honor: Allied Assault War Chest.
Memoria
Men of War: Assault Squad
Men of War: Red Tide
Men of War: Vietnam Special Edition
meridian
Messiah?
Might and Magic® 6-pack
Might & Magic 9
Monkey Island™ 2 Special Edition: LeChuck's Revenge™
Mortal Kombat 1+2+3
Mount & Blade
Mousecraft
Myst
neo scavenger
Neverwinter Nights Diamond Edition
Neverwinter Nights 2 Complete
Night of the Rabbit
Nosferatu: Wrath of Malachi
Nox
Oceanhorn: Monster of Uncharted Seas
Oddworld: Abe's Exoddus
oddworld: Abe's Oddysey
Oddworld: New 'n' Tasty
oddworld stranger's wrath
Omikron: The Nomad Soul
Outlaws + A Handful of Missions
Overlord + Raising Hell.
paper sorcerer
Panzer General 2
Phantasmagoria
PIER SOLAR AND THE GREAT ARCHITECTS
Pillars of Eternity: Hero Edition
Pilot Brothers
Pinball Gold Pack
Pixeljunk Shooter
Police Quest Collection
Police Quest: SWAT 1+2
Post Mortem
Primordia
Prince of Persia
Prince of Persia®: The Sands of Time.
Quest for Glory
Rayman 2: The Great Escape
Rayman 3: Hoodlum Havoc
Realms of Chaos
Redline
Redneck Rampage
Resonance
REVOLVER360 RE:ACTOR
Risen
Risen 2: Dark Waters
Robin Hood: The Legend of Sherwood
Rogue Legacy
Sacred Gold
Sacred 2 Gold
Sam & Max Hit the Road
Sea Dogs
Secret of Monkey Island™: Special Edition, The
Settlers® 2: 10th Anniversary, The
Shadow Warrior (2013)
Shadowgate: Special Edition
Shadowgrounds Survivor (dupl)
Shadowrun Dragonfall
Shadowrun Returns
Shadows: Heretic Kingdoms
Shelter 2 Special Edition
Shivah
Shovel Knight
Silver
SimCity 2000
SiN Gold
Sir, You are being hunted
Sokobond
Space Quest 4+5+6
S.T.A.L.K.E.R.: Call of Pripyat.
STAR WARS™ Galactic Battlegrounds Saga
Star Wars™: Jedi Knight™ - Jedi Academy™
Star Wars: Jedi Knight - Dark Forces 2
Star Wars™: Jedi Knight™ II - Jedi Outcast™
Star Wars: Knights of the Old Republic
STAR WARS™ Knights of the Old Republic™ II: The Sith Lords™
Star Wars™: Rebel Assault 1 + 2
Star Wars: Republic Commandos
STAR WARS™: TIE Fighter Special Edition
STAR WARS™: X-Wing Special Edition
STAR WARS™: X-Wing vs. TIE Fighter
Stealth inc. 2: A Game of Clones Deluxe
Strike Suit Zero: Director's Cut
Stronghold Crusader HD
Sunless Sea
System Shock 2
Tales of Maj'eyal
Telepath Tactics
Teslagrad
Tex Murphy: Tesla Effect
Thief™ Gold
This War of Mine
Tomb Raider 1+2+3
Toonstruck
Toren [Upcoming]
Total Annihilation Commander Pack
Transistor
TRINE ENCHANTED EDITION
Ultima 1+2+3
Ultima 4-5-6
Ultima Underworld 1+2
Unmechanical
Unreal Gold
Unrest
Urban Chaos
Vampire: The Masquerade - Redemption
Vanishing of Ethan Carter
Wasteland 2
Wing Commander 1+2
Wing Commander: Armada
Wings remastered.
Wings of Prey: Special Edition
Witcher: Enhanced Edition
Witcher 3: Wild Hunt, The [Upcoming]
Witcher Adventure Game
Wizardry 6+7
Xenonauts
Ys I & II Chronicles+
Ys VI: The Ark of Napishtim
Y's Origins
Zak McKraken and the Alien Mindbenders
Zeus + Poseidon
Zork Anthology

Been so busy not testing the Galaxy beta that I almost forgot to post here. Almost.
Round #2, Guess #22: Dead Synchronicity: Tomorrow Comes Today

2nd try - Panzer General 2

R2G8:
Rayman 3: Hoodlum Havoc

PIER SOLAR AND THE GREAT ARCHITECTS

And it's still not found !

So let's close round 2 and start round 3

Same rules, except there are now 3 new keys in play, thus a total of 4:

a) carried over from round 2 , 1 key with 3 related items, something about one of the greatest perceived challenges (or boundaries) of our species

b) new KEY, 1 game
c) new KEY, 2 games, not on GOG anymore
D) new KEY , 3 games

Good luck

R3 guess #1: Red Faction.

Also, the list has been (or, better said, is being) updated.

(Many thanks to mrkgnao for creating MaGog search engine.)

Unless I am mistaken 1 is, only one, somewhere in 1 of the keys. not a) obviously :-p