For what it’s worth, I think the Swiss receptacle system (
SN 441011) is extremely elegant: it consists of four receptacle types: 10A and 16A, in single-phase and three-phase. 10A plugs fit into 16A sockets (not so special), but the thing that is unique (as far as I’m aware) is that single-phase plugs fit into three-phase sockets.
This is extremely practical, for example in laundry rooms, which often have three-phase sockets for the washer and dryer, but which then accept a modern single-phase heat pump dryer without any adapters.
Standard 2-pin Europlugs (CEE-7/16, 2.5A) fit into them, too (the standard requires sockets to accommodate them) but not standard European grounded CEE 7/7 (Schuko/F) or the 16A 2-pin (CEE-7/17) European plug.
Old versions of the standard had some exposed-metal hazards, but sleeved pins have been required for years, and recessed sockets are now required for all new installations. (In the past they were required only in wet spaces.)
It’s curious that all of the newest outlet standards (like the new ones in Brazil and South Africa) are based on the IEC 60906-1 socket, which itself is a tweaked version of the Swiss socket. (All mutually incompatible, of course…)