Technically all of them work already, just with subpar UI. If you follow a Lemmy community on Mastodon by searching for it like a user, the community’s posts show in your Mastodon timeline.
Each community post appears as a Mastodon post boosted by the community “user”. Threaded replies all work.
To make a post to a community, you tag the user in any top-level Mastodon post.
There’s a survival game called Grounded that’s basically this but even smaller. And a coop story action/adventure called It Takes Two that does the same.