We present some notes on Milner's calculi of processes. We interpret the terms of these calculi as transition systems. We introduce a calculus, called MEIJE, built upon a monid of synchronized actions, and illustrate some general semantic notions: we show the equivalence of this calculus with some others, and we give an implementation in a calculus restricted to purely atomic actions. We show the universality of MEIJE with respect to the notion of effective transition system, and sketch its expressive power with regard to synchronization operators. Finally the concept of a subcalculus is illustrated by means of the description in our language of the class of rational parallel place machines.