pss (bzz whispered) is a swarm network service offering incentivised internode messaging using kademlia based deterministic routing.
phase 0 comes with priorities and an easy to use api exposed to RPC. you can subscribe to messages and peers using geths new pub/sub (available via websockets and ipc).
Swarm kademlia routing implements an efficient unicast address based messaging system. While whisper's architecture offers a nice trade-off between efficiency and anonimity, it is lacking the case when strong anonimity is not required, but predictably low latency transfer is. Public chatrooms, or convo between nodes that do not mind leaking this fact (the content is always safe due to end-to-end encryption).