There are no out-of-the-box implementations except in JS.
How can anyone even figure it by themselves if there is not a high-level explanation of what is that they should be figuring out? I wanted to ask nostr:npub1xpuz4qerklyck9evtg40wgrthq5rce2mumwuuygnxcg6q02lz9ms275ams to implement it on Yana, but I didn't even know how.
It's weird because he has an infinitely huge feature list and is implementing everything he can see, but perhaps he didn't realize the outbox model was a possibility?