As known, we use MeteoIO in our GEOtop 2.0. Despite the fact that we implemented most of the same capabilities inside GEOtop directly. And despite we also reimplemented the same (and in some case more articulate possibilities inside JGrass-NewAGE). Many the reasons: having alternatives to compare is good; it is not possible to keep pace in every subject necessary to built a modeling system, and having someone doing things for you is the essence of the success of a open source project; the JGrass-NewAGE system is not yet at the stage to be interoperable with GEOtop tools. In any case Mathias Bavey and Thomas Egger did an excellent work in documenting MeteoIO with this paper appeared in GMD, one of our journals of election.
The project is open source, well designed, constantly maintained and evolved, in C++. Have a nice reading.