I remember reading a book by Ron Klinger(who happens to be Australian, but is part of the commonwealth nonetheless). He used Acol. I guess some Commonwealth countries use it too. If I ever play bridge abroad, it is best that I get acquainted with the governing laws of the country in question, as well as the most common bidding system in that country. Sometimes the laws and play are virtually identical to the US (as in Canada), other times they are quite different (as in the United Kingdom.) Poland is the most fascinating- many players there play a weak and strong combined club, called Wspolny Jezyk (Polish Club, to non-Polish speakers.) I think that system is by far my favorite. I will have to find an online bridge partner from Poland so we can play the same system.