Apparently this tool is made by Telelogic. Anyone ever heard of it?
I work for Telelogic (though not on the Tau Product line).
Basically it's a communications protocol testing tool based on the international TTCN-3 standard (http://www.etsi.org/ptcc/ttcn3download.htm):
Find out more about Tau Tester here:
Read about TTCN-3 here:
Hope this helps.