I haven't used Kafka in production, but we use NATS in Spawner[1] and I find it quite pleasant to work with. It gives you some basic but powerful messaging constructs (request/reply, queue groups, temporal decoupling via Jetstream) and then gets out of your way.

[1] https://github.com/drifting-in-space/spawner

NATS is very powerful. The author has like 25 years of experience building messaging systems and NATS has been around for a long time. The streaming component is slightly newer but I'd say it does the same job as Kafka but much lighter footprint with zero deps.

Side answer to your side question: not sure for NATS, but Redpanda is trying to be a lightweight drop-in alternative

And RedPanda uses WebAssembly as an execution engine to keep with the WASM theme here. https://redpanda.com/blog/wasm-architecture

Redpanda also appears to be being a bit more stringent about some of the correctness and consistency stuff.

It's great actually, you can run it with pretty much no maintenance overhead. I have been using it in prod in multiple companies for years now