Na at 0,0,0 and Cl at ½,0,0: rock salt, four formula units, from two lines of input. Step 18 of 18 of the symmetry tutorial, worked in a live 3D view.
Molecular point groups with their operations and character tables, the 230 space groups with a cell builder, and the 17 wallpaper and 7 frieze groups drawn live. The tool needs JavaScript, and WebGL2 for the 3D views; these are the pages it offers: