The Binding of Isaac came out twelve years ago, if you're looking to feel a little older, but only now is it looking to add proper online co-op. A big update is coming to The Binding of Isaac soon, as revealed by the game's executive producer.
Tyrone Rodriguez posted over on Twitter/X a screenshot of what a matchmaking screen looks like, confirming that online co-op is indeed coming. Rodriguez also stated that this is only coming to Repentance, so you'll need to own the DLC if you want to play with friends online.
<social>https://twitter.com/tyronerodriguez/status/1707522206358761705</social>
Still, it's interesting to see that even 12 years on, one of the most popular and influential roguelikes of all-time is getting significant updates.