This is covered in the wiki but some of the high-level features are:
Full-distributed (no broker)
Built-in security – messages are authenticates and encrypted end-to-end (node-to-node)
Publications and subscriptions can have multiple topic strings (subs only match if all required topics are present)
MQTT-like wild-card matching (+ and #)
MQTT-like retained messages, but with TTL
Forms mesh overlay network with hop-by-hop routing based on subscriptions
Automatic subnet bridging- container and virtual network friendly
Supports UDP multicast and unicast
Built-in support for RPC
Built-in support for data series
Simple protocol designed to be implementable on MCU’s
Protocol itself is payload agnostic
Not all of these features are currently exploited in the RMW layer.