The mod adds co-op to the game: the story, a run or a colony, shared with friends.
How it plays
Replaces summons with a lasting session: you and up to three friends play the whole game together, with no resummoning after every boss or death.
Seamless Co-op
Runs on its own save with Easy Anti-Cheat off. Install it exactly as the mod page says, and never go online with anti-cheat on while it is installed.
Unofficial fan mod. Back up your saves.
Get it on Nexus Mods
How it plays
Explore Skyrim as a group. Quest progress follows the party leader, who does the talking with NPCs. Keep your other mods few: they are not guaranteed to sync.
Skyrim Together Reborn
Unofficial fan mod. Back up your saves.
Get it on Nexus Mods
How it plays
Everyone runs the same colony at the same time, kept in sync on every machine. Other mods you add have to support it.
How it plays
Multiplayer on OpenMW, the open-source Morrowind engine. Quests and the world state are shared on a server that you or a friend host. You need the original game files.
How it plays
Open-source multiplayer: build bases and follow the story together in one shared ocean. Download it from the project page only, never from mirror sites.
How it plays
Each player flies their own ship through the same solar system; the time loop and what you find out are shared. Installed with the Outer Wilds Mod Manager.
Quantum Space Buddies
Unofficial fan mod. Back up your saves.
Get it on GitHub
How it plays
Grow one factory across the star cluster together, each player in their own mecha. Installed from Thunderstore with a mod manager.
How it plays
Climb the Spire as a party: everyone plays their own deck, and the fights are shared. Subscribe on the Steam Workshop.
How it plays
Real co-op in one shared world: the same pixels burn, flood and blow up for every player.
How it plays
Join friends through Steam invites and explore Pharloom together; enemies sync through an add-on. An early release, so expect rough edges.
Shared servers to drive or fly around on together. Fun with friends, but not a co-op story.
How it plays
A shared server where everyone flies their own missions in one universe, career mode included. A sandbox to share, not a guided co-op story.
How it plays
Drive the same maps with friends on servers you join or host: free roam, races and events. A sandbox, not a co-op campaign.
Every game here is single-player on Steam, or only has summon-style co-op, and a fan mod turns it into co-op. We list a mod only when it works today: we compare its latest release with the game's latest patch on Steam News. A mod released after that patch is marked as updated. When a game is patched and the mod hasn't caught up within 30 days, we take it off the list until it does.
Each entry has a scope line, because co-op mods differ a lot. "Full game together" means you play the whole game as a group. "Partial campaign" means some of it is shared and some isn't: in Skyrim Together, quests follow the party leader. "Sandbox servers" means a shared world to mess around in, not a story played together.
Someone re-checks every entry by hand at least every 90 days. After 90 days without a check an entry is marked "not rechecked recently", and after 180 days it disappears. We leave out mods that are in alpha or abandoned, games that now have official co-op (Stardew Valley, Teardown and The Binding of Isaac all do), and standalone Steam games such as Sven Co-op.
We link only to each mod's official project page on GitHub, the Steam Workshop, Thunderstore or Nexus Mods, never to mirrors or re-uploads. These are unofficial fan projects: they can break saves, and a mod that touches online play can clash with anti-cheat. Back up your saves and follow the install steps on the mod's own page.
For most mods on this list, no: they don't touch any online service. Elden Ring's Seamless Co-op is the one to be careful with. It runs on its own save with Easy Anti-Cheat off, so the risk comes from installing it wrong and going online with anti-cheat on. Follow the steps on the mod's page.
Yes. Every player needs the game and the same mod version. When a game update comes out, wait for the mod to catch up before you play, or stay on the game version the mod supports.
There's no mod that does proper co-op for them right now. The Witcher 3's online mod lets you explore the world together, but quests and enemies aren't shared, so we don't count it as co-op.
Someone re-checks every entry by hand at least every 90 days, and each status is worked out again every day against the game's latest patch. The date on each card is the last time someone checked that mod.