Abiotic Factor fucking RULES. I've put quite a few hours into co-op and I don't usually seek out co-op in games (I also have a single player world with a fairly extensive farm base). The early game has such an amazing aesthetic and vibe that you truly don't know what you're getting into, especially if you went in almost completely blind like I did.

Zomboid would be another obvious pick for me, although I still haven't played co-op or multiplayer at all. I'm scared about servers not having certain mods I keep in my list I guess.