macjanitor_1.2.1.dmg.sit???

I just downloaded mac janitor and when I click on the file there is no default app to open; it asks me to choose an application. What is the "sit" extension? Has anybody else had trouble with this? Am I not able to use this software? Tia

.sit files are archives, sort of akin to zip files. it should open in Stuffit Expander (which comes with every Mac.)

Open stuffit expander, and then drag the archive over to the icon on the dock.

Thanks...it worked! (of course)