I wonder, what would it be worth to the world if there were an actor framework for multiple languages that offered interopability between languages? IIRC Akka.net and Akka aren't compatible with each other.

Dapr is designed to offer this afaik (https://github.com/dapr/docs/blob/master/concepts/actors/REA...). It uses GRPC and HTTP to allow clients and services of the virtual actors in various languages (C#, Java etc.) to communicate.

Also ProtoActor which uses GRPC to be cross-platform between C#, Go and Kotlin:

https://proto.actor/

wasCC [1] goes in that direction.

It supports all languages that compile to wasm.

Very early stage project, though.

[1] https://wascc.dev/