The request header parser microservice project was my second Node/Express app. It accepts API requests, parses out the header of the request and returns some information back to the requester. The endpoint returns the requester's user agent, language, and IP address.
The Server-side Development with NodeJS course on Coursera was also very useful for this project. It covers Node, Express, MongoDB, and Mongoose, so you can use it to learn everything you might need for the M, E, and N parts of the MEAN stack.