Project management in Emacs. Managing groups of files together, especially code.
These libraries (though they may be at varying stages of development) have the goal to be full project-management solutions. Each offers its own way of thinking about a project, or uses a project definition created by another piece of software.
It is probably not useful to use more than one of these at the same time, for the same project.
These libraries address some aspect of project management without trying to be all-in-one solutions. You may find it helpful to use several of these at the same time, even in addition to the all-in-one solutions in the section above.
These libraries have little to do with project management per se, but are handy when dealing with many files or buffers at once.