This is an experimental library meant to provide some additional functionality to C11 threads. The background for this comes from the serious issues C++ suffered while trying to improve their threading APIs while suffering backwards-compatibility and structure upgrade problems:
C++ is attempting to use templates and other techniques to try and save on effort. This library takes a different approach, instead using an enumeration with 65,536 reserved values [0, 65'535] for the standard, and 2,147,418,112 reserved values [65'636, 2'147'483'647] for implementation-defined attributes. Each value of the enumeration corresponds to a structure that describes something for the thread to use.
You can find the the library documentation here (https://ztdthread.rtfd.io).