There are 2 file types use the .NUT file extension:
1. Squirrel Script
A NUT file is a text file that contains Squirrel code written in the Squirrel programming language. It is a script used as a plugin to extend functionality of a program and for scripted events in video games.
Since there is another file type with the ".nut" extension, you can look at the file size for an indication of what type of NUT file you have. NUT files containing a Squirrel script rarely reach 1MB whereas NUT video files are larger than 1MB.
Updated: December 2, 2016
2. NUT Video File
Video file saved in the NUT Open Container Format, a container format similar to .AVI, .ASF, and .MKV; supports several different audio and video codecs as well as subtitle information.
The NUT format was developed by the MPlayer, FFmpeg, and Libav teams. However, it did not gained wide popularity and therefore is an uncommon video format.
Updated: April 17, 2015