ntk is a fast and lightweight GUI toolkit for the Non-DAW application
suite. It is a build requirement of Non, and is distributed along with
Non source code. It is packaged separately for SlackBuilds.org because
other software (such as Qtractor and Fabla) can use it, plus in order
for Non-* to build, ntk must be installed first.

So, install this first, and then build and install Non.

The only official download is available as a git repository. In order
to standardise this SlackBuild, a snapshot of the git repository as of
28/09/2020 has been posted to slackermedia.info.