CMPR is a Graphical Manual Powder Indexing and Powder Diffraction Toolkit written in Tcl/Tk by Brian Toby which links a variety of tools together. One of the very nifty features is the graphical display of HKL lines over raw data, then (using scroll bars of the cell axis and angle values) and moving the overlaid HKL line positions in near real time.

This is useful when you have a cell from Electron Microscopy or similar analysis, or where you know some of the cell values but need to experiment with the data to get a cell and spacegroup in ways that auto-indexing programs do not allow.

This is also useful for teaching purposes and it can easily be shown why determining the cell and spacegroup from powder data can be so non-trivial. It also allows intuitive graphical manual indexing.

An Overview of the program is described at http://www.ncnr.nist.gov/programs/crystallography/software/cmpr/