Are you ready for an engineering joke? The international standard for mains plugs and sockets, IEC 60906-1, is used only in Brazil.
If you've ever travelled with electronic gadgets internationally then the idea of a standard power socket probably appeals. Non-travellers too will benefit from the effort that has gone into designing this system. The two main features I like are that its round prongs line up relatively flat, making it difficult to injure yourself stepping on it, and the compact size enabling sockets to be packed more densely (especially compared to the UK and Australian systems) in walls and powerboards.
The standard was published in 1986, and given the lack of enthusiasm so far I don't expect to see it adopted by any countries other than Brazil in the near future.