It's not ideal but we have been using a program called XtalDraw on windows for this, to display the different lattices and to build up the content of the unit cell from a small molecule of 2 or 3 atoms by applying the different space group symmetries. The students can edit the coordinates file (not pdb format unfortunately) to change the symmetry and see what happens in a hexagonal lattice as p1 goes to p3, p6, p6(1) etc.  I put figures made starting with a screenshot of xtaldraw, and some of the simple coordinates files we used (plain text)
in http://sb20.lbl.gov/berry/xtaldraw/ . The figures look 2D because in projection, but the lattice is actually 3D, rotatable by mouse or arrow keys.
In principle I guess the same thing could be done with O or coot generating symmetry mates within a sphere, and using real pdb files.

Chen Zhao wrote:

Dear all,

I have been trying to search for some softwares/applications that can display the crystal space group "lattice" based on
the input of cell dimension and space group. Ideally, it can also apply the arbitrary symmetry operation to a molecule
with given orientation and position in the unit cell. It would be perfect if it can output a PDB file. Does anybody
heard of something like that?

I know it might not be too hard to be realized with a script simply modifying the coordinates, but unluckily I am not a
programmer. And actually, even some simple PDB files of different space group, in which molecules are represented as
dots, would be very helpful.

Thank you so much!

Sincerely,
Chen Zhao