I'm wondering if there are any .NET libraries (ideally open-source) that deal with guitar chords (e.g. given either a chord or a set of fret/string combinations it can retrieve the corresponding fret/string combination or chord respectively).
I'm having some trouble searching because "C#" is a note and there is a concept of "programming" musically as well.
It seems to me that you're actually asking for a collection of digitized guitar chords, rather than a particular library. I think that if you look for a guitar chord database, you will find several downloadable programs that incorporate a database, but I haven't found a freely available db of chords yet. Unfortunately freebase doesn't seem to include chords.
It may be that all chords are calculable based on a breakdown of their names. In that case you would want a library, or at least the formula, instead of a db. But I don't believe this is the case. There is some explanation of the naming here though.