Crystal and Structural Chemistry: http://www.uu.nl/en/research/crystal-and-structural-chemistry
Distributed Software: http://www.crystal.chem.uu.nl/distr
Crystal Growing: http://www.cryst.chem.uu.nl/lutz/growing/growing.html
Twinning: http://www.cryst.chem.uu.nl/lutz/twin/gen_twin.html
Ton Spek's PLATON software: http://www.cryst.chem.uu.nl/platon
Ton Spek's powerpoint presentations: http://www.cryst.chem.uu.nl/spek/ppt.html