The official link for GRADISTAT Version 9.1 is available through the K. Pye Associates downloads page
GRADISTAT-PRO: A fully revised version with expanded functionality is currently under development by the original authors. gradistat v 91 link
GRADISTAT is a widely used Microsoft Excel-based program for the granulometric analysis of sediments (sand, gravel, mud). It was developed by Simon Blott. The official link for GRADISTAT Version 9
The program is highly valued for its ability to process approximately 50 samples per hour and provide both tabular and graphical outputs. Michigan Technological University GRADISTAT software - Kenneth Pye Associates Ltd gradistat v 91 link
Official Source: The software is maintained by Kenneth Pye Associates Ltd, where the standard version can typically be downloaded.