More open-source math

Some of this might be a repeat, I don't remember.

• Modelica is a language for defining mathematical models, which are then interpreted by an arbitrary simulation engine.  Very cool and declarative.
• OpenModelica is one such simulation engine, and is open-source.  There are lots of other simulation engines on the market - engineers spend lots of money on them - and seemingly most of them now have bolt-on Modelica interpreters, which makes sense.
• OpenModelica also exports code things in UML (or stub code or something) for writing your own simulations.  Or something.  The point being that this kind of declarative interface is what interests me.  ModelicaML is the keyword.
• There's all that, and then Mathics, which is an open-source (Python-backed) interpreter of the Mathematica language.  Not all of Mathematica is supported, but it's an interesting project.

All this is sort of the outline of some kind of general approach to mathematics that I see myself as girding for.