With a friend we’ve built this [1]. Usability has been our main focus, though we ended up having very good perfs (millions of mps out of the box, usually 2x to 10x kafka). We provide REST and WebSocket APIs, + a simple to implement binary protocol for the most demanding workloads. It’s in Go so very light and rock solid in stress tests. We provide trivial to implement and understandable usage patterns for exactly once processing. We’re currently working on HA and cloud integration. And we’re looking for community feedback BTW ! :)

[1] https://github.com/dataptive/styx