This is an ever expanding list of adventure games not present currently on steam (which I inititally posted on another PnC steam group now mostly dead), doing it for my own pourpose but decided to share it in case people have more titles to add (note that some of these ARE available on GOG though). They are not neccesarily all have to be point and click but I will mostly leave out hidden object games, interactive narrative movies (TellTale style games) or any other subgenre, also no 1st person exploration+puzzles ala Myst. Games have being organized by developers or in some cases publishers, you can see the year it came out and the platforms it did.

Can´t you find that one amazing PnC adventure you play once? Tell us about it and I´ll try to add it. Here´s the list:

Defunct since 1998.

• Ace Ventura: The CD-Rom Game - (1996) PC

Defunct since 2006

• Countdown - (1990) DOS
  
• Amazon: Guardians of Eden - (1992) DOS

No info

• Heaven's Dawn - (1995) DOS

Defunct since 2011

• U.F.O.s aka GNAP - (1997) PC/Mac

Italian developer, still in active.

• Martin Mystère: Operation Dorian Gray - (2005) PC
  
• Belief & Betrayal - (2007) PC
  
• Diabolik: The Original Sin - (2009) PC/PS2/NintendoDS/PSP/Wii

Small studio from Florida, USA that started out as a one person company. They developed several license games like Spongebob and Nancy Drew. Went defunct in 2011.

• Agatha Christie: And Then There Were None - (2005) PC/Wii
  
• Agatha Christie: Murder on the Orient Express - (2006) PC
  
• Agatha Christie: Evil Under the Sun - (2007) PC/Wii

No information

• The Immortals of Terra: A Perry Rhodan Adventure - (2008) PC

Defunct since 1996

• (As Publisher) Wayne's World - (1993) DOS

No info

• Touché: The Adventures of the Fifth Musketeer - (1995) PC/DOS

Acquiered by Sierra on 1992, which after many buy outs ended up on Vivendi. Eventually all previous Coktel Vision properties and remaining stuff was acquiered by Mindscape, which exited the videogame industry in 2011.

• Fascination - (1991) DOS/Amiga/Atari
  
• Bargon Attack - (1992) DOS/Amiga/Atari
  
• Ween: The Prophecy - (1992) DOS/Amiga/Atari
  
• Lost in Time - (1993) DOS
  
• Gobliiins - (1992)
  
• Gobliins 2: The Prince Buffoon - (1992)
  
• Goblins Quest 3 - (1993)
  
• Gobliiins 4 - (2009)
  
• The Bizarre Adventures of Woodruff and the Schnibble - (1995) PC

Acquiered by CentreGold in 1994, then by Eidos in 1996,then in 2006 by Rebellion Developments whom rebranded it as Rebellion Derby and was shut down on 2010 after many failure games (they made Rogue Warrior and the 2010 Alien vs Predator, among other "gems"). Rights of these games should belong to Rebellion which is mostly a comicbook company this days with their future goals set on movie for the 2000AD IPs (Judge Dreed).

• Curse of Enchantia - (1992) DOS/Amiga
  
• Universe - (1994) DOS/Amiga

Closed down on 1997. The rights to their most famous game, I Have No Mouth But I Must Scream (a true classic you can get here on Steam and GOG) ended up in Nightdive Studios

• Darkseed - (1992) DOS/Amiga/MAC/SegaSaturn/PS
  
• Dark Seed II - (1995) PC/Mac/SegaSaturn/PS

Creators of Another World and Flashback. Defunct since 2004

• Future Wars: Adventures in Time - (1989) DOS/Amiga/Atari
  
• Operation Stealth aka 007: James Bond - The Stealth Affair - (1990) DOS/Amiga/Atari
  
• Cruise for a Corpse - (1991) DOS/Amiga/Atari

Company went defunct in 1996, all their games were published by Psygnosis, which still exist as a financial entity owned by Sony, they do not develop or publish games any more.

• Innocent Until Caught - (1993) Amiga/DOS
  
• Innocent Until Caught 2: Presumed Guilty/Guilty - (1995) DOS
  
• The Orion Conspiracy - (1995) DOS (first game to ever use swear words)
  
• The Gene Machine - (1996) DOS

Difficult to find info due to the name being used for several active companies. Assumed defunct.

• Nippon Safes, Inc. - (1992) DOS/Amiga
  
• The Big Red Adventure - (1995) DOS/Amiga
  
• Tequila & Boom Boom - (1995) DOS

Defunct since 2001

• Rise of the Dragon - (1990) DOS/Mac/Amiga/SegaCD
  
• Heart of China - (1991) DOS/Mac/Amiga
  
• The Adventures of Willy Beamish - (1991) DOS/Mac/Amiga/SegaCD

Defunct since 2011. A few of their other games are on Steam.

• NiBiRu: Age of Secrets - (2005) PC
  
• Next Life aka Reprobates - (2007) PC
  
• Tale of a Hero - (2008) PC

Acquired by Sony in 2021

• Alien Incident - (1996) DOS

While their last game was made in 1999 there is no info on the company having shut down

• Scooby Doo Mystery: Blake's Hotel+Ha Ha Carnival - (1995) SegaGenesis
  
• Blazing Dragons - (1996) PS/SegaSaturn
  
• Duckman: The Graphic Adventures of a Private Dick - (1997) PC
  
• Beavis and Butthead Do U - (1999) PC

As a developer it went defunct in 1989, but continued as a publishing label for Activision, whom are belive to keep holding all their assets and rights. They were most famous for the Zork series.

• Leather Goddesses of Phobos! 2 - (1992) DOS

No information

• Mutation of J.B. (game only exist in Slovak and German languages)- (1996) MS-DOS

Defunct since 2002

• Dark Earth - (1997) PC

Defunct since 1996

• Bud Tucker in Double Trouble - (1996) DOS
  
• (Publisher) Trick or Treat - (1994) DOS

Defunct since 2009

• Teenagent - (1994) DOS/Amiga

No information

• Hopkins FBI - (1998) PC/Linux

Supposedly defunct since 2004, they only made 3 games. Electronic Arts publish their games so they could be the rights owners for all we know.

• The Lost Files of Sherlock Holmes: The Case of the Serrated Scalpel - (1994) DOS
  
• The Lost Files of Sherlock Holmes: The Case of the Rose Tattoo - (1996) DOS

Took me some digging to find out, some places it states that it´s defunct since 1986, but the date made no sense with the game I know about them. Eventually found out that the company released two erotic games and decided to focus on that, they are now named Redfire Software for anyone curious about it.

• Chewy: ESC from F5 - (1996) DOS/PC

Defunct since 1998. Currently all their assets belong to Bandai UK

• Hook - (1992) DOS/Amiga/Atari

Still in active and still developing adventure games

• Igor: Objective Uikokahonia - (1994) DOS
  
• Hollywood Monsters - (1997) PC

• Discworld - (1995) DOS/Mac/PS/SegaSaturn
  
• Discworld II: Missing Presumed...!? - (1996) PC/PS/SegaSaturn
  
• Discworld Noir - (1999) PC/PS

Active and still developing PnC adventures, this one it´s just missing from Steam.

• The Silver Lining - (2010-2011) PC

No information

• The Adventures of Down Under Dan - (1995) DOS

Founded in 1998 and from Italy, there´s no info on if it´s still active or defunct.

• Tony Tough 2: A Rake's Progress - (2006) PC

Stoped developing and publishing in 2012, but still exist as a legal entity for Sony.

• The City of Lost Children - (1997) DOS/PS

No information

• Legacy: Dark Shadows - (2004) PC

Spanish dev that went defunct in 2011, the other two games from the Fenimore Fillmore series are published on Steam by Casual Brothers dev/publisher, a company with his headquarters in London, England were at least one person who worked on the fisrt Fenimore game still works there.

• Fenimore Fillmore's Revenge - (2008) PC

Still in active and still developing adventure games. All their games are on steam except for this one.

• Lure of the Temptress - (1992) DOS/Amiga/Atari

Defunct since 2001

• Ripley's Believe It or Not!: The Riddle of Master Lu - (1995) DOS/Mac
  
• Orion Burger - (1996) DOS/Mac

Defunct since 2008, although most of the rest of their games are on Steam

• The Black Cauldron - (1986) DOS/Amiga/Atari
  
• Code-Name: Iceman - (1989) DOS/Amiga/Atari
  
• The Colonel's Bequest - (1989) DOS/Amiga/Atari
  
• The Dagger of Amon Ra - (1992) DOS/PC
  
• Conquests of Camelot: The Search for the Grail - (1990) DOS/Amiga/Atari
  
• Conquests of the Longbow: The Legend of Robin Hood - (1991) DOS/Amiga
  
• EcoQuest: The Search for Cetus - (1991) DOS
  
• EcoQuest 2: Lost Secret of the Rainforest - (1993) DOS/PC
  
• Freddy Pharkas: Frontier Pharmacist - (1993) DOS/Mac/PC
  
• Torin's Passage - (1995) DOS/PC/Mac

German developer who got bought out by The Games Company (yeah, someone actually made a dev company called like that) and then went solo again once this one declared insolvent, four years later on 2014 Silver Style would declare itself insolvent. Besides Simon 4 and 5 they also made The Dark Eye: Demonicon (here on Steam republished by another company) and a tabletop game also in The Dark Eye universe.

• Simon the Sorcerer 4: Chaos Happens - (2007) PC
  
• Simon the Sorcerer: Who'd Even Want Contact?! - (2009) PC

No information

• Fable - (1996) DOS/PC

Defunct since 1999

• Star Trek A Final Unity - (1995) DOS/MAC

Australian dev. defunct since 2018, however, the employees founded Purple Lamp, which has release the two remakes of Spongebob platform games as well as making Sea of Thieves.

• Undercover: Operation Wintersun - (2006) PC

Acquired by Sierra on 1996

• The Beverly Hillbillies - (1993) DOS

The Worms guys, most of their catalogue is on Steam

• Nightlong: Union City Conspiracy - (1998) PC/Amiga

This one is a curious one. It´s a british company with their headquarters in Hong Kong specialized on investing on animation, but there are no registers of the company to be found anywhere except for the fact they try to do a game, they hired american comedians Martin Short and Eugene Levy and after that the company disappears completely.

• Creature Crunch - (1996) PC

Defunct since 1999

• The Neverhood - (1996) PC/PS

Defunct since 1999. This company was created by Sierra On Line ex-employees.

• Ringworld: Revenge of the Patriarch - (1992) DOS
  
• Return to Ringworld - (1994) DOS
  
• Blue Force - (1993) DOS

No information

• The Pink Panther: Passport to Peril - (1996) PC

Bought by Virgin Interactive in 1992. Bought by Electronic Arts in 1998 alongside Virgin. Merged with into EA Los Angeles (later Dreamworks Interactive, later Danger Close Games). Close down in 2013. Rights of other Westwood series like Comand and Conquer have shifted internally on EA and recently we got a Blade Runner from Nightdive Studios. So at this point is completely unclear who owns the rights, most likely EA.

• The Legend of Kyrandia: Book One - (1992) DOS/PC/Mac
  
• The Legend of Kyrandia: Book Two - Hand of Fate - (1993) DOS/PC/Mac
  
• The Legend of Kyrandia: Book Three - Malcolm's Revenge - (1994) DOS/PC/Mac

Defunct since 2011

• Benoît Sokal's Paradise - (2006) PC/NintendoDS

Defunct since 2012, their latest games are on Steam, but not this two.

• So Blonde - (2008) PC
  
• So Blonde: Back to the Island - (2010) Wii/NintendoDS

Mostly an animation french studio, but they own the IP and decided to make the game themselves

• Stupid Invaders - (2000) PC/Mac/Dreamcast

PD: Thinking about looking for a way to maybe add genre on the mix, but it may take much space and make the list less easy to read on the go, we´ll see.