I was disappointed when MS discontinued Axum, which I found pleasant to use and thought the language based approach was nicer than a library based solution like Orleans.

The Axum language had `domain` types, which could contain one or more `agent` and some state. Agents could have multiple functions and could share domain state, but not access state in other domains directly. The programming model was passing messages between agents over a typed `channel` using directional infix operators, which could also be used to build process pipelines. The channels could contain `schema` types and a state-machine like protocol spec for message ordering.

It didn't have "classes", but Axum files could live in the same projects as regular C# files and call into them. The C# compiler that came with it was modified to introduce an `isolated` keyword for classes, which prevented them from accessing `static` fields, which was key to ensuring state didn't escape the domain.

The software and most of the information was scrubbed from MS own website, but you can find an archived copy of the manual[1]. I still have a copy of the software installer somewhere but I doubt it would work on any recent Windows.

Sadly this project was axed before MS had embraced open source. It would've been nice if they had released the source when the decided to discontinue working on it.

[1]:https://web.archive.org/web/20110629202213/http://download.m...