Pydet is a plug-in for PyMOL capable of visualizing Delaunay tessalations of atom sets.
The article about PyDet, including install instructions:
Rafael Ördög: PyDeT, a PyMOL plug-in for visualizing geometric concepts around proteins
PyDeT source: PyDeT.py
The free version of PyMOL can be found here.
For generating the tesselations PyDeT will also need a copy of QHull installed on your system.
Nascent is a protein-protein physical interaction network mapper utility. You can download its standalone versions here or access the online (webservice) version.