The GLYCAM Molecular Modelling Library (GMML) assists in a variety of molecular modelling tasks, with a particular focus on carbohydrates. It works particularly well with the AMBER suite of molecular simulation programs.
To obtain GMML, see its github site. To learn more about its structure, see the online documentation by Doxygen. You might also want to check out GEMS.
The old source for GMML is also available. It is being refactored, and the current GMML might not yet possess all the functionality of the old version.