As far as I can tell N.World was a modelling and animation (and rendering) package comparable to Maya. See this press release from 1996: http://findarticles.com/p/articles/mi_m0EIN/is_1996_August_6...

"[... ] our tools were used to model the characters for Super Mario 64".

I bet SM64 was written in C++.

EDIT: ... and possibly large chunks of it in C, too, since the C++ compilers always seemed to lag several months behind the C compilers on new platforms, and SM64 was a launch title.