And I'm not talking about a REAL app that would replace or alternate GitHub's functionality. I'm talking about an app that extends and uses the functionality of GitHub, according to developer.github.com/apps/marketplace

I'm not really familiar with developing an application as an extension of another application, but based on what I have read it can support node.JS as its programming language.

Some of these extensions if you look into the website show supports of other languages but I have no way of knowing or confirming if its the app itself that were written in these languages or they support applications that are written in these languages?

So, what say you, the experts on this area, are GitHub Apps only written in node.js? If not, can they be written in other languages and what are these languages?