StuffIT, that became Allume, that became digital river is becoming less and less relevant on Mac OS platform. Part of the reason for that, of course, is the policy of the manufacturer, that requires signing up, buying things, etc. It’s nearly impossible to find the free StuffIT expander, for those rare moments when you need it.
In any event, here is a direct link to the StuffIT download page. I had to give out a throw-away e-mail address to get it.