Event sourcing is already widely used as app to app communication. But few realize that it is plausible to take that paradigm and use it for module to module communication in-app.

That line serves as reminder to utilize that, not to exclude non in-app event sourcing

I'd love to see a good example of in-app module-to-module event sourcing.

By module to module, do you mean between very loosely decoupled systems such as microservices, or closely associated things like queues and method calls in a single-process process?

Both in-process, inter-process, and inter-machine. The event sourcing technique really helps decouple components, reduce the need for higher order state.

I work with TypeScript on daily basis and I'm in the middle of building this library to help with event sourcing and other stuffs. https://github.com/Kelerchian/florcky

I'll be working with rust, C++, and C# in a few weeks due to professional demand and I might get somewhere with event-sourcing using those language.

In the long run we might be utilizing wasm and ffi to introduce universal protocol for event sourcing.