Online document sharing

Hope this is the right forum for this - if not, I apologize. I'm trying to find a free online document sharing service that provides a function similar to Word's "Track changes." I know some (Google, Zoho, etc.) have a revision history function but that's too broad. They either don't show exactly what has been deleted or show that an entire document has been deleted and re-entered. Anyone know of an existing free service that has a traditional track changes kind of feature?

Thank you.