You'll see on the Downloads tab in OptimalSort that it currently says "You will need Excel on Windows to use the Macros," however this isn't strictly true anymore. Office 2011 for Mac supports macros and appears to work well with the spreadsheet. Earlier versions unfortunately do not work. I'll make sure we update that message on the Downloads tab.
Hopefully the spreadsheet functionality (correlation scores based on standardised category labels) will make it into the OptimalSort web application itself some time in the near future. We have been planning it for a long time but have struggled to prioritize the development. Now that we have new versions of Chalkmark and Treejack released, it is something that we will take another look at shortly.
In the mean time, hopefully you have a Windows PC nearby, or a Mac running Office 2011. Sorry for the inconvenience.