As correctly noted in the comments selection of server-side
language depends on the task.
If you are working in real time and strong adhesion of the interface with the server (the user to Open a window with new data if you change them on the server using the direction from the server to the user) that Node.js (optimal), etc., RoR,Python.Net (Except PHP, it is possible to do this but this is an unnatural act of masochism, which sooner or later will lead to "neuroses" and "psychoses" of the server).
If you anticipate a high workload of the project and not "storing" as computing functions (meaning not 2 * 2, and more) to choose from RoR,Python.Net.
Successful examples of the application of Node.js are raindrop.io