Here are the games that I own that Playnite lists as co-op in alpha-order: Ancestors Legacy
Ascent
Baldur's Gate I & II
BAttlestar Galactica Deadlock
Black Desert
Blazing Beaks
Borderlands 1-3
Broforce
Cassette Beasts
Castle Crashers
CAst Quest II and III
City of Ages
Daemon X Machina
Dark Envoy
Dead Island
Devil May Cry 5
Diablo IV
Dragon Age Inquisition
Dynasty Warriors VII
Elder Scrolls Online
Elite Dangerous
Final Fantasy XV
Forza Horizon 4
God EAter I & II
Grand Theft Auto V
Guid WArs II
HellDivers
It Takes 2
Just Die Already
Legos games
Mech Warriors Mercenaries V
Monster Hunter Rise
Monster Hunter World
Rise of the Tomb Raider
River City Girls
RWBY
SAints Row 2 and IV
Mega Drive Classics
Deathwing
Streets of Makorocho
STreets of RAge 4
TAles of Berseria
Tiny Tina's Wonderlands
Titanfall 2
Unravel 2
WAr Mongrels
Vermintide II
A Way Out
Where Winds Meet
A lot of those I'm pretty sure aren't co-op, but I've only got that filter selected... Some are local 2 player, which we can play with parsec's screen and controller sharing in which case only one of us needs to own the game.
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