I spent about two evenings on it
that's how technology navigation is learned, the hard way
CP2K is one of the better free dynamic chemical simulators.
Always on my mind is: chemical simulators, electronics simulators, building design simulators (including many simulators, rich in pertinent information), raytrace simulation (physical light appearance simulators / 3D cad design even game design), city simulators. they are too large to just "release in mathematica" (would have to be just one installed add-on, for most)
they have huge interfaces (popular 3D game design interfaces are a good example) and mathematica is poor at that. huge code bases (mathematica is good at that but isn't connected for many reasons)
the simulator code is custom and the rich information locked in it. the math is poor in these (often so is ability to modify). there is little way to interact with Mathematica (a few file format converters - usually very limited in ability, cut&past - very limited). many ask about MathLink but few or none have ever produced any product that links up with any large simulator.
mathematica, despite not being "higher level than C", can compile and run code "as good or better". but it's ability to offer "large interfaces" is poor. the people willing to tackle "rewriting a simulator in mathematica" and provide a thorough MathLink interface: is about none. we don't have a mathematica download area with mathlinke'd simulators, not even one. CDF format is really only good at (trivial) problem exhibition.
this is a predicament that i frequently think about
a ton of custom simulators that can't do math and have no "central language"
a best mathematics, algorithms, code program which can't do "interfaces" (interfaces much due a cross platform lib issues, software wars, etc)
mapping is a good example of a technology that was simulated by custom apps that somehow gets "active" in mathematica
mapping companies made special large interfaces and multi-layered maps and mapping format files. these became orchestrated systems of standards of "how to transmit various mapping information". finally mathematica offers mapping data that has drivers capable of reading that information which is rich which (simulator specific information of how it is used)
the result: mathematica has powerful mapping simulation (though little interface). no circuit simulation.
but what about the rest? good question.