The Brigham Young University ISOTROPY Software Suite server, at web address https://iso.byu.edu/, is also an international treasure. It provides a collection of \(\approx 20\) utility programs, which are largely motivated by representational analysis. Some of these offer very sophisticated analyses and graphical tools. The backbone of the site is the ISOTROPY program, which, to the best of my knowledge, is not in general distribution, but can be run online from the web site. Note that each utility entry has an extensive help page with documentation and, at least where I have looked, an annotated example. One of the really neat tools built into this website is a visualization program called IsoVIZ where one can vary the distortion modes generated by the programs and see how the structure is changed by the mode or combinations of modes.
As noted before, if a CIF is generated on this web site that contains displacive, occupancy or magnetic distortion modes, when the CIF is read by GSAS-II, the distortion modes are converted to constraints that can then be used in refinements.