I'm very tempted to say HoMM 3, but I will instead say Overcooked (first game).

Portal 2


It's only 2 player co-op... but you *have* to work together on the co-op maps.

If you'd like to have fun session go for Jazz Jackrabbit 2 Coop. Definitely worth for playing. Hidden gem :)

A universe can be a terrifyingly lonely place. My suit, my space ship, my scanner, my trusty multifunctional tool, which allows me to mine needed materials, dig holes to avoid terrible storms on strange alien worlds or fend off Sentinel robots, predators or weird horrors spawned by the demented source code of the universe.

Alone... I set out to explore this strange universe, where suns orbit cluster of planets and moons, where alien species are almost everywhere - across millions of light years - but don't have much to tell me. Where history is recorded in ancient monoliths, where old monuments are found in asteroid fields, where an increasingly insane creator god AI made worlds of metal and wire and code.

On a lush world, I built a base. A home, made of wood and steel and concrete. Some chairs, some lights, some potted plants. A porch where I sit and watch the ever moving sun sink behind the horizon, and after that, the stars.

Music is playing. Music I made, with devices so clever they're almost magical, built into the world, built into the code, built from materials I found in my lone journeys. I sit there, watching the sun set - together with a friend. His real self is hundreds of miles away, but his suit, his ship, his multifunctional tool are here right now. "Let's do this mission, you do the scanning, I keep the Sentinels of your back" he says. And "Nice tune, by the way."

(No Man's Sky)

First, happy anniversary. But i am not a Coop Player, strictly single player. The last time was ca. 25 years ago Bomberman(?) on Console which was wicked fun. Though i only played Borderlands solo, i can imagine all those titles would be great in coop. I do love vinyl though, and the covers look gorgeous.Nice to see even gamers are onto it...

Saints Row: The Third

Are you looking for some entertainment for these long autumn evenings? Good old game, you can play with friends and discuss your adventure over a cup of hot glögi?

Stronghold is the offer, you long for. There are no heroes, but cunning and plotting medieval lords. There is no place for magic, even though you can meet unwelcome guests with a shower of boiling oil.

Powerful editor allows to create any location, you could imagine. Gather with friends and decide, where to settle your next noble dispute.

Would you like to protect the historical castle, which you have visited together on vacation? Let those memories of real-life archery contest become your inspiration.

Or build a wooden outpost in a smelly bog? Like wetlands on the road to your summer cottage, where you have seen a mighty bear in the evening mist.

Place a wolf den by your friend's village, while he is not looking. Or prepare some devastating fires in the event timeline.

Then invite a jester or traveling fair, as a nice surprise and compensation. We are in alliance, after all.

If you want to save precious time and rush right into action, a lot of existing maps are at your service.

Be ready for a siege, plan economy well and discuss combat tactics with your allies. This game can be really challenging at times.

Site your granary, sire! And let the fun begin! 8)

By the way, it's awesome medieval music is worth being released on vinyl.

I haven't had the chance yet, but I'd die to play Blood in co-op mode!

Best coop game in my mind is TowerFall Ascension

My current favorite Co-Op game would be Deep Rock Galactic, but it isn't available on GOG. So for games that are available on GOG, I would go for Dying Light or Towerfall.

I would recommend Neverwinter Nights: Enhanced Edition as a perfect co-op game to play, especially considering that it's part of the Anniversary Sale!

A venerable classic given new life, the base game of NWN:EE offers three campaigns of 3E Dungeons and Dragons experience, and with the character creation and henchman system, you have a great deal of leeway to tailor the experience as you see fit. That said, though a solo run of the base game offers plenty of value all on its own, D&D is *meant* to be played with others, it's in online co-op that the game really shines. In co-op mode, no longer are you restricted to choosing a single player class and only one additional companion among a few limited pre-fab choices; with multiple players, you and your friends have even greater freedom to create the party of your dreams, and to shape campaigns' events in accordance with the choices you make as adventurers. This freedom expands even further with the addition of expanded and user-created content, allowing you and your companions to quest beyond the boundaries of the base game, and if you feel so inclined, even into adventures of your own making!

In the dangerous and exciting world of Faerun, the challenges ahead of you are great and many; why not bring along a few friends to watch your back, and share in the glory?

I really enjoy No man's sky and think it'd be a cool choice.

TowerFall

One classic which comes often to mind is Warcraft 1 or 2.
But what comes also to mind is the criminally underrated Freespace 2.
Also got some fond memories of the old Double Dragon beat'em up games. :)

Serious Sam, the First and Second Encounter.

Also waiting for someone to use that source code to make a source port to get the mods rolling out.