Especially if you want one-to-many connections, exactly once delivery and push/ pull consumers, it is worth checking out nats [0, 1]. It is very performant. There are clients for Javascript, Python, Rust and Go [2].
(I am not affiliated with them)
that's just not true. NATS does have neither at-least-once nor exactly-once. NATS Jetstream has at-least-once, but it does not have flexible topics anymore like NATS. It's two completely different things.
You may be thinking of NATS Streaming which was a predecessor to JetStream. It was indeed a standalone thing that used NATS under the hood. JetStream is now baked into the NATS server.