I’ve been enjoying Slipways, a space exploration/economy game with the tagline “Build vast space empires. Still be done in time for lunch.” Roughly speaking, Slipways is a mini version of Stellaris the way Polytopia (also recommended) is a mini version of Civilization.
But Polytopia is a multiplayer game, and I like casual multiplayer games like that. And Stellaris and Civilization support multiplayer too. And even though Slipways isn’t a combat game, or really a competitive game in any way1, I think you could make a good cooperative multiplayer game out of it: two empires trying to achieve the highest possible score together.