Second Life's 3-D navigation, menus and editing, from the camera control for the AV to constructing #D virtual objects with primitives.
I think that’s why SL is still so popular because it got the interface right, non-technically inclined people can learn to build rudimentary objects in a couple hours and its enough to hook many of them into becoming content builders.
Another would be FoxBase+/Mac for under a meg of object code the UI for data management and screen/form building was great. I got ugly when MS came in and standardized it into FoxPro for Windows compatibility.
The oldest best UI was the Print Shop on 8-bits changed the face of cork bulletin boards since.