Last night's co-op stream we took a look at How to Survive 2, a game that just hit early access last week on Steam. The new game supports four player online co-op, but also 16 player persistent communities where folks can work together towards surviving.
The game clearly has a ways to go, as actually getting a co-op game started is a bit tricky. You'll need to bring up the communities menu and then allow certain friends into a community. Once that is done they'll be able to see your game in a list of available games.
Here's the stream recap with lots of good information in 3 player co-op.