1. Yes you can say that Modelica has some heritage from ACSL. (See https://www.modelica.org/publications/papers/esm98his.pdf https://www.modelica.org/publicatio

1. Yes you can say that Modelica has some heritage from ACSL. (See https://www.modelica.org/publications/papers/esm98his.pdf https://www.modelica.org/publications/papers/esm98his.pdf) but the short story is that some simulation language creators decided to form a uniform modeling and simulation language together instead of working on their own initiatives, resulting in Modelica. 2. Not really. Usually modified versions of DASSL/CVODES and friends are used by Modelica tools. In Cellier and Kofmans's book on simulation QSS gets prominent display and some of the research at Berkley Labs has been using QSS to some extent, but it is far from mainstream.