I am not entirely sure. I had bunched dapr together with Istio, as a "service-mesh" layer utilizing side-car pods to mesh the different pieces of your service.

Just browsed it again, and there seems to be a bit more tooling in place. But I fail to see something like Mats in its feature list, though.

Mats is about endpoints which can invoke other service's endpoints. It is "messaging with a call stack", simplifying how you can code messaging-based inter-service communications. Pub/sub is not the same, and (synchronous) REST/gRPC is what Mats explicitly is an alternative to.