I'm not super familiar with Akka beyond high-level/actor model so I can't competently compare the two. NATS can be used to implement an actor model and has a similar philosophy to Akka core in terms of delivery semantics (i.e. no real guarantees - https://doc.akka.io/docs/akka/2.1/general/message-delivery-g...).

Looking at Akka Streams, it appears to be more in line with Liftbridge, though I'm not totally sure. Liftbridge (like Kafka), is a message log, so messages do not get acked or removed from a stream (unless removed due to retention limits or compaction). I'm not sure if that's the case with Akka Streams.

I'm curious what your needs are around exactly-once delivery. From what I can tell, Akka only supports at-least-once semantics and is of the opinion that exactly-once isn't really possible as such (which is an opinion I agree with, but that's a more nuanced discussion). https://www.lightbend.com/blog/how-akka-works-exactly-once-m...