Esterel is developed at CMA and INRIA in Sophia Antipolis.

(CMA Sophia-Antipolis)

CMA is the Center for Applied Mathematics of Ecole des Mines de Paris. It is a research unit based in Sophia-Antipolis. Besides Esterel, CMA develops the Jazz circuit design language and reactive programming languages.
See the Reactive Project web site.
CMA also has a control theory group.

(INRIA Sophia Antipolis)

INRIA is the French National Institute for Research in Computer Science and Control.
It is a scientific and technological institute operating under the dual authority of
the Ministry of Research and the Ministry of Industry.

CMA is actually hosted by INRIA in its Sophia-Antipolis site

The development of Esterel takes place in a common project between CMA and INRIA. This project was called Meije until Y2K. It has split into two new projects: TICK, which develops Esterel and verification technology, and MIMOSA, dedicated to mobile process calculi and programming languages.