Hyena is a library of useful GUI and non-GUI C# code, originally used in Banshee.
** It is not API stable, and so is not installed to the GAC.**
Applications using it should make a local copy of whatever components you use. That is, you should consider Hyena a build-time dependency, not a run-time, since at run-time your app will contain a copy of Hyena.
There are variables defined in the pkg-config files that contain assemblies and files needed for a given component of Hyena (eg hyena, hyena.data.sqlite, and hyena.gui).
pkg-config --variable=Assemblies hyena
pkg-config --variable=Files hyena
You can look at PDF Mod for an example of how to use Hyena: