Actix was built initially using its own runtime and has gone over many iterations including a runtime change to tokio over its lifetime. In the past, building asynchronous actors with actix has been a huge pain and felt like a big after thought.

Ractor is nice, and I've used it in the past. A couple things differ between kameo and ractor:

- In ractor, messages must be defined in a single enum – in kameo, they can be separate structs each with their own `Message` implementation. This means messages can be implemented for multiple actors which can be quite useful.

- In ractor, the actor itself is not the state, meaning you must typically define two types per actor – in kameo, the actor itself is the state, which in my opinion simplifies things. As someone mentioned in a comment here, it was a bit of a turn off for me using ractor in the past and I didn't fully agree with this design decision

- Ractor requires the `#[async_trait]` macro – kameo does not.

There may be other obvious differences but I'm not super familiar with ractor besides these points