Modia.jl is built by Hilding Elmquist, Martin Otter and their collaborators. These are some of the best folks in the world - Hilding's thesis in 1978 described equation oriented modeling. It had to wait until computers became powerful enough in the 90s to become broadly usable.
https://people.inf.ethz.ch/fcellier/Res/Soft/Dymola_engl.htm...
We've had the benefit of learning from them and their presentations at JuliaCon and collaborating. More is coming. In the meanwhile - do see this JuliaCon talk by Hilding: