Always online. You can start a mission and not call for reinforcements. Sometimes people like to play solo or with just one friend.

Rez and Fez. Similar names, very different games.

I didn’t see this mentioned but it’s a great couch co-op indie game. Has a 93% rating on steam. https://store.steampowered.com/app/252110/Lovers_in_a_Dangerous_Spacetime/