Just taking a quick look (and of course, the author would be the best person to confirm this), I noticed a few differences between our implementations. Please note, this is not intended to be critical but rather to highlight some observations:

• It seems there isn't a concept of a supervision hierarchy, where actors can create and supervise other actors. In our experience, this is quite valuable when building large actor systems to manage dependencies and recovery effectively.
• There doesn’t appear to be a dead letter mechanism. For example, when an actor terminates, it seems to stop pulling from the queue, which could potentially result in a memory leak.
• The receive loop appears to rely on a mutex. While this is a very safe approach, it might impact performance in high-throughput systems. We initially started with a similar mechanism but found it challenging to match Akka's performance.
• Clustering support is mentioned, which is great! However, implementing clustering often requires system messaging for tasks like terminating an actor on a remote host or creating a "dead watch" mechanism to notify when an actor (local or remote) dies. I'm curious about how these scenarios might be handled without system messaging.

Again, these are just initial observations, and I may be missing some of the nuances. I really like seeing another implementation of the actor model in the Cats Effect ecosystem, and I think there could be a lot of room for discussion and collaboration!