An open-source Java viewer for chemical structures in 3D. It runs in four independent modes: * an HTML5-only web application utilizing jQuery, * a Java applet, * a stand-alone Java program (Jmol.jar), and * a "headless" server-side component (JmolData.jar). Jmol can read many file types, including PDB, CIF, SDF, MOL, PyMOL PSE files, and Spartan files, as well as output from Gaussian, GAMESS, MOPAC, VASP, CRYSTAL, CASTEP, QuantumEspresso, VMD, and many other quantum chemistry programs. Files can be transferred directly from several databases, including RCSB, EDS, NCI, PubChem, and MaterialsProject. Multiple files can be loaded and compared.