As someone evaluating Kafka for the first time, it would be useful to know what Hermes provides other than Kafka already does. After glancing at the homepage I see the REST api and the fact it is push based. Honestly I don't see how it would fit on my use case but interesting project nonetheless.

> exactly once delivery

Kafka is known to provide exactly once semantics - given your producers and consumers follow some rules, notably being idempotent. When ingesting from Kafka Stream API, it is actually exactly once delivery. There are a couple posts on confluent.io explaining how they achieve this (sorry, currently on mobile, can't copy-paste without having an outburst on how unusable touch devices are for me).