Honestly a lot of them start out as or still contextually imply "males" in the US, but can be used gender neutrally as well now too. Like "how you guys doing" vs "hanging out with the guys."
It's interesting isn't it? "Guys" can include women, and can even be a group of only women, but you can't talk about a single woman as a guy - "I snogged this gorgeous guy last night".
Using "guys" for a group of only women works only in 2nd person. You can say "I love you guys!" to a group of women, but you can't say "I was hanging out with the guys" when talking about the same group.
Which just so happens to be the perfect segue for me to pitch my proposal to make 'cunt' the de facto (gender neutral, naturally) pronoun/collective pronoun.