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Worms come to mind :)

Mount your friends, Battleblock Theater, maybe something like Awesomenauts?

Obligatory castle crashers

This

Been wanting for myself, but still too much imo.

Bomberman, any version that support local multiplayer. Bomberman 93 is a staple on any gaming nights with my friends.

Dungeons & Dragons: Chronicles of Mystara is great if you like beat 'em ups. One of the best that I've played at least.

Thief Town is supposedly rather fun as well. I have a spare key for it, so just send me a message on steam and I'll give it to you.

Worms, any of the 2D ones are good.

Jamestown, and it also supports a wide range of input devices, so even if you don't have a lot of controllers it's easy to play.

Hidden in Plain Sight. http://store.steampowered.com/app/303590/

Lovers in a dangerous spacetime might be smth for you (no Mac but splitscreen coop)
Edit:
Monaco seems to have couch-coop too (though I havn't tried it that way)

Maybe Crawl.

Wyv and Keep. It's two-player coop, but the rest will have a blast mocking the players when they inadvertently kill each other. And maybe then taking turns to kill them instead.

Also, Magicka?

Towerfall Ascension is a godlike game with 2player coop multiplayer or 2-4 player versus.
Broforce
Spelunky works well, but it's harder than fun - but multiplayer makes it easier with caskets to "revive" your friends
Hidden in Plain sight
Crawl
Sorry if any of these are not available for mac

worms
metal slug games
hammerwatch
blazerush
castlecrasher
race the sun (just single player but you can turn to play it , it's more like a dodge game but funny check steam shop page)

Heard of Eon Altar?

Smartphones are used as controllers, not sure but I think you setup a LAN and it doesn't require an internet connection.

Move or die?

I was going to say one of the Jackbox Party Packs (1 & 2), but they need a connection. Not sure if that's good for you.

crimsonland: mac, shared screen, up to 4 players
gauntlet: shared screen, up to 4 players
broforce: mac, shared screen, up to 4 players
trine 1-2-3: mac, shared screen, up to 3 players