Protein-Ligand Interaction Profiler
Whilst this is not a Mac application I thought I'd mention it since it seems a very nice implementation.
The Protein-Ligand Interaction Profiler (PLIP) is a web service and command line tool for fully automated characterization of non-covalent interactions between proteins and ligands in 3D structures.
You can either upload a PDB format file or use the search facility to use a PDB by protein, ligand or enzyme-commission number. You can combine multiple search terms to be more specific (AND search).
I used the PDB code 3EQB, the software correctly identified two ligands, ATP and the more interesting ligand CHEMBL485945.
You can view the results using the embedded 3D molecule viewer JSmol shown in the image below.
PLIP is based on a python command-line application. In case you plan local mass/batch processing, you may want to use this one directly. The source code can be found on PLIP on Git Hub.
I first tried this out on my desktop machine and it worked beautifully, I then tried it out on my iPad and iPhone and the website functioned exactly as expected.