These are just the demo files.
Express API -- Express' core API. Considering that a lot of the API are properties or self-explanatory methods (i.e. req.body or res.redirect()), it's pretty easy to get through.
Sequelize API -- If you want to use MySQL, MariaDB, MSSQL, or PostgreSQL.
Mongoose API -- If you want to use MongoDB.
Nodemon -- The tool to use for development. Automatically restarts the server when files in you app change.
Morgan -- Logging middleware.
RFS -- Rotating File Stream for production logging (integrates with Morgan).
Lodash -- Client-side and server-side utility library.
Superagent -- For making HTTP requests to other services.
Nodemailer -- For connecting to mail servers and sending mail.