"Mate", "china" (its rhyming slang equivalent) or pal are used as greetings by friends (and occasionally cheeky strangers) to men, in my experience, in England and Southern Africa at least. As a reply, those words are used mostly by strangers who are trying to be amiable towards men, e.g. a taxi driver's response to a request for assistance might be "OK mate". Towards women, "madam", "ma'am", "missus", "miss" or "love" are more likely in replies from strangers, in my experience.
The only American use of "mate" for "friend", that I have encountered, is in the song that goes "It's simply great, mate, waiting on the levee, waiting for the Robert E Lee."