Here is a list of all documented namespaces with brief descriptions:

NFST	The Feature Selection Toolbox 4 library: every library component – data access, criteria and classifiers, search algorithms, result trackers and the global infrastructure – lives in this namespace
Nfst4_cli	Internals of the fst4 command-line tool: its type aliases, the option record, the run pipeline with its result types, the CLI-specific observers and adapters, and the output emitters