This paper describes a system for designing
and classifying actor languages.
This system, named {\em Actalk},
which stands for {\em act}ors in Small{\em talk}-80,
is based on some minimal kernel introducing actors into Smalltalk-80.
The Actalk kernel extends passive and sequential objects activated by
synchronous message passing
into active and concurrent actors
communicating by asynchronous message passing.
This defines a sub-world of actors
embedded into the Smalltalk-80 programming
language and environment, which is left unchanged.
The Actalk kernel is composed of only two Smalltalk-80 classes.
Simulating current actor languages or designing new ones
is achieved by defining subclasses of these two kernel classes.
Consequently all such extensions are implicitly classified
by the inheritance mechanism
and unified into the Actalk environment.
We are currently extending the standard Smalltalk-80 programming environment
to design a specific one dedicated to Actalk concurrent actors.

In this paper,
the motivations and the goals which led to design the Actalk system
are first discussed.
Then the structure and implementation of the kernel of Actalk is detailed.
The very good integration of this kernel
into the Smalltalk-80 programming
language and environment is demonstrated through some examples.
Interests and limits of combining objects with actors are then discussed.
In the last part of the paper,
we demonstrate the expressive power of the Actalk kernel
by extending it to simulate the two main actor computation models and
programming languages,
namely, the Actor model of computation,
and the Abcl/1 programming language.
Related and further work is summarized before concluding this paper.