Mercury offers a comprehensive range of tools for structure visualisation, the exploration of crystal packing and statistical analysis of ConQuest geometric searches.
A base version of Mercury is available as a free download.
Basic Mercury features include:
a full range of structure display styles, including displacement ellipsoids (N.B. displacement ellipsoids will be displayed for CIFs or SHELX res files which contain Uequiv or Uij values only)
the ability to measure and display distances, angles and torsion angles involving atoms, centroids and planes
a number of output options for saving displays
functionality for creating and displaying centroids, least-squares mean planes and Miller planes
location and display of intermolecular and/or intramolecular hydrogen bonds, short nonbonded contacts, and user-specified types of contacts
the ability to build and visualise a network of intermolecular contacts
the ability to calculate, display and save the powder diffraction pattern for the structure on view
the ability to display unit cell axes, the contents of any number of unit cells in any direction, or a slice through a crystal in any direction.
Very helpful software for study.
I found mercury really a helpful tool to assist me in all problems related to crystallographic structures.
A superb program for chemical crystal structures. To use Mercury you need a CIF or MOL file containing the measured crystal stucture of a certain chemical solid. There are no universal CIF/MOL collections freely available, but for a start try finding TGZ-zipped teaching_subset_cifs.tgz file from the CCDC web site. (= the author of this program) Even better if you get real ORTEP structure cifs from the web sites of real chemistry journals.