A recent publication DOI describes an update to the popular molecule viewer UCSF Chimera
UCSF ChimeraX is next-generation software for the visualization and analysis of molecular structures, density maps, 3D microscopy, and associated data. It addresses challenges in the size, scope, and disparate types of data attendant with cutting-edge experimental methods, while providing advanced options for high-quality rendering (interactive ambient occlusion, reliable molecular surface calculations, etc.) and professional approaches to software design and distribution.
The application can be downloaded here http://www.rbvi.ucsf.edu/chimerax/download.html
It is important to note that ChimeraX is not backward compatible with Chimera and does not read Chimera session files. It has been tested on MacOS X 10.12. The ChimeraX user interface is implemented in Qt, offering a native-like look and feel on each platform. ChimeraX is largely implemented using Python, an interpreted programming language. To manipulate these very large datasets interactively, ChimeraX uses memory-efficient data structures combined with high-performance algorithms implemented in C++. MacroMolecular Crystallographic Interchange Format (mmCIF) is the preferred format for atomic data in ChimeraX, mmCIF replaces the aged and more limited PDB format and offers a number of advantages.