A collection of multiple TeX libraries.
Some of them are published to CTAN, but not all.
For those published, the documentation can easily be found on CTAN (not necessarily of the latest version).
Otherwise, documentation might be available in https://github.com/user202729/TeXlib/tree/main/doc.
You need to compile the TeX file from source.
To generate the index file properly, you need to use gind.ist -- the easiest way is to use latexmk
with the provided latexmkrc file.