The original Le Havre is by Uwe Rosenberg.
You can play this at https://harbortowngame.herokuapp.com/
The client is React based and can be run with react's dev-server using npm run-script clientonly. The client must be compiled (with npm run-script build) to be served by the server. The src/common directory contains code that will be invoked from both client and server, and includes most of the actual game logic. Because it can be invoked from either, it cannot import either (though it still has many callbacks passed in from either as dependency injection).
Developing client-only requires nothing but react. Developing the server requires MongoDB, a gmail account to send notifications from, and an RSA private key. Search for process.env in the server code to see how all of these apply.
If you want to get a sense of internal structure, run the drawDepGraph.sh script in src.