OpenMesh is a generic and efficient data structure for representing and
manipulating polygonal meshes.

The main features of the underlying data structure are:
* No restriction to triangles meshes, handle general polygonal meshes.
* Explicit representation of vertices, halfedges, edges, and faces.
* Efficient access to the one-ring neighborhood of a vertex.
* Ability to handle non-manifold vertices (like two faces meeting in only one
  vertex).

WWW: https://www.openmesh.org/