libmsym is a C library dealing with point group symmetry in molecules.

Features:
* Determine, symmetrize and generate molecules of any point group as well
  determine/select subgroups. Get symmetrically equivalent elements and
  symmetrize translation of any any element in a molecule.
* Generate character tables for any point group (complex characters form
  reducible representations)
* Generate SALCs of real spherical harmonics with any angular momentum for
  point groups with real characters (Ci, Cs, Cnv, Dn, Dnh, Dnd, Td, O, Oh,
  I and Ih), as well as symmetrize orbitals, determine partner functions etc.

WWW: https://github.com/mcodev31/libmsym