For PC's
DS Visualizer This is a highly functional, sophisticated program for viewing and analyzing primarily protein molecules. You can draw and import small molecules, too. You will need to register. Choose "academic", "research", and "student" in the drop-down boxes. Use your GMU email address.
DS ViewerLite is the earliest version of DS Visualizer and is very simple and easy to use. You might try it before trying the full DS Visualizer, which has become extremely complex.
ChemSketch/3DViewer ChemSketch is a structure drawing program with the capability of rendering the drawings into a 3DViewer. The drawing program is not the easiest to learn. Here are some instructions for the full package.
For Mobile Devices
WebMO is a web-based computational chemistry package. It allows drawing or import of molecules that can be geometry-optimized. It will calculate partial atomic charges, molecular orbitals, and electrostatic potential energy maps. Free with registration for up to 9 atoms. WebMO is available for both iOS and Android.
Mobile HyperChem for iOS allows drawing and display of molecules.