Not Proven is indeed almost unique to Scotland - though it has occasionally been returned in Canada in the past, and was the verdict voted for by one Senator in Clinton's perjury trial, though his verdict was formally recorded as one of not guilty anyway. It doesn't get around double jeopardy, however: it is an acquittal verdict, legally equivalent to not guilty. (Originally, Scots juries were instructed to return verdicts of either proven or not proven; proven was replaced with guilty, but not guilty was added as a third verdict rather than replacing not proven.)