We present the basics of the ESTEREL reactive model of synchronous parallel systems. We illustrate the ESTEREL programming style, based on "instantaneous communications and decisions '' through the example of a mouse handler. We briefly describe the ESTEREL formal semantics and show how programs can be compiled into finite states sequential machines for efJicient execution. The up to date implementation is described together with the ESTEREL environment, including simulation, and verification and validation tools. Finally, we report on some ESTEREL uses in various contexts.

We present a new synchronous programming language named SL based on Esterel, in which h ypothesis about signal presences or absences are not allowed. Thus, one can decide that a signal was absent during one instant only at the end of this instant, and so reaction to this absence is delayed. Esterel \causality problems" are avoided at the price of replacing strong preemptions by weak ones. An operational semantics based on rewriting rules is given and an implementation is described which allows either to directly execute programs, or to produce automata.

Reactive systems are interactive programs that react continuously to sequences of activations coming from the external world. Reactive programming leads to a new programming style where one programs in terms of reactions to activations and reasons in a logic of instants. This paper describes an extension of the C programming language called RC (for 'Reactive C') to program reactive systems. The language RC is described, then some programming examples are given to illustrate the reactive approach. The main RC notions come directly from the Esterel synchronous programming language. Finally, the Esterel and RC languages are compared. KEY WORDS Reactive system C programming language Parallelism

SugarCubes is a set of Java classes used to implement dynamic, reactive, event-based, parallel systems. SugarCubes can be seen as a low-level basis upon which more complex reactive formalisms can be implemented. It also provides a convenient framework for prototyping experimental extensions to various reactive formalisms. SugarCubes is freely available on the Web.