Kivy looks very nice but NUI is a very different beast (I'm the author). The main difference being that even though NUI is a complete multi-plateform framework that uses OpenGL for rendering, it has a strictly C++ API.
I've been using the name for 13 years or so but a number of other libs started using the acronym unfortunately (New UI, Natural UI, etc.). I should have been more vocal and public about the lib from the beginning :-).
If you want to see apps built with NUI I just released reChord: http://bit.ly/rechord And also some very nice music apps with NUI: http://intua.net/products/beatmaker2/ http://www.whitenoiseaudio.com/apps/genome-midi-sequencer/ http://www.whitenoiseaudio.com/apps/bleepbox/