Recently, an updated cooperative mod Bannerlord Together was released for the RPG sandbox Mount & Blade II: Bannerlord.
One user acts as the host player and owns the "simulation", while the other connects, receives the save automatically, and enters the same world:
You will see each other on the campaign map as full-fledged squads. Cities, villages, AI armies, battles, diplomacy and much more are synchronized between the two PCs. The mod is in active development [...]
Now the mod supports joint battles: players with their armies will be able to participate in the same battle.
The "Bannerlord Together Live Battles Alpha" mod for Mount & Blade II: Bannerlord has already been published on Nexus Mods.