Everything you’ve ever wanted to know about ISO paper sizes (such as A4), which is used worldwide. Well, except in North America. Maybe one day they’ll catch up. Maybe not. The article talks about the resultant difficulties of exchanging documents between North America and The Rest Of The World, and also notes the different hole punch standards.
It’s related to the uptake of metric, of course. So how many countries are resisting going to metric? According to this FAQ a survey some time ago concluded not many: Liberia, Burma, and the USA.
Mind you others, like the UK, haven’t totally switched, and still use imperial for things like distances.