Nice to cross your path, I got the first one to kickstart myself some years ago (and still struggling with evaporation / condensation).

Would you recommend the second to introduce a colleague to OpenModelica? He is into gPROMS but will lose access to the software at retirement.

Sidenote: invest in software with freedom to operate and good knowledge reusability.

Modelica by Example is the most recent and free, so I would recommend that.

Are you aware of any books like your "Introduction to Physical Modeling with Modelica" but for readers without a background in EE, math, physics? I am looking for something for a mediocre SWE like myself. It doesn't have to be Modelica; I could try learning MatLab or Mathematica, etc.

Well if you are interested in the intersection of software engineering and technical computing, I'd recommend Julia. I'm currently working on JuliaSim which is a Modelica like system built on top of Julia. So Julia might interest you as a programming language and then you could pick and choose what aspects of things like ModelingToolkit if you are interested in the engineering, math and physics aspect or you can just stick to the software/programming aspects of Julia.