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 :-).
"Open source software library for creating NUI applications, running on Windows, Linux, MacOSX, Android and iOS"
I guess that is why I searched for NUI and I probably found your lib. I don't remember that I have heard that term "NUI" before.