BuildQSAR is a free program designed to help the QSAR practitioner on the task of building and analyzing quantitative models through regression analysis. The main part of the program is a spreadsheet, in which the user can enter with the data set composed by the structure definition of the compounds, one or more types of biological activity values and many physicochemical properties.
JSmol (free) is a very popular versatile JAVA-based program that allows structures to be examined in detail, including molecular orbitals. If keyword HTML is used, MOPAC will write a simple web-page that can be opened using JSmol. For examples, see Molecules, Solids, and Animations.
Other GUIs for MOPAC2016™ (either untested or unsupported)
Avogadro (free) is an excellent editor for preparing MOPAC input data-sets and for viewing results. Runs on Windows, Mac, and Linux.
Molden (free) is a good pre/post processing program of molecular and electronic structure that runs on Windows, Mac, and Linux. Z-matrix editing of geometries.