Chairman of the Modelica Association which develops and maintains the object-oriented modelling language Modelica (since 2000).
Contributions to the free Modelica standard library, such as MultiBody (3-dim. mechanics), Rotational (1-dim. rot. mechanics), StateGraph (hierarchical state machines), Blocks (input/output blocks), Media (large media library), Fluid (basic components for thermo-fluid pipe flow).
Commercial DLR PowerTrain library to model power trains of vehicles (since 2003).