Elfo is another actor system. Check The Actoromicon.
Note: although it's already actively used in production, it's still under development. Wait for v0.2 for public announcement.
To use elfo, add this to your Cargo.toml:
[dependencies]
elfo = { version = "0.2.0-alpha.13", features = ["full"] }
[dev-dependencies]
elfo = { version = "0.2.0-alpha.13", features = ["test-util"] }