Pick a space group, give it a cell and put atoms in it: the general positions are generated, the glide planes and screw axes are drawn where they fall, and the structure can be exported as a CIF.
The 230 groups are addressed by their International Tables number, and the settings of a group — other axes, another origin — are the same page rather than a near-duplicate of it.
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: