The Actalk testbed is designed to help understanding, classifying, designing, combining, and experimenting with various OOCP languages and constructs.
Actalk is implemented and integrated within Squeak environment. The testbed includes the kernel which models basic OOCP model (that is serialized active objects and asynchronous message passing), and various extensions in order to simulate various OOCP languages and constructs.
They implement various models of activity (serial, quasi-concurrent, concurrent...), communication (asynchronous, synchronous, eager, express...), and synchronization (to control/delay acceptance of messages).
Actalk stands for active objects, or also actors, in Smalltalk.