There is no such thing as separated client and server app in the isomorphic era, there are only environments (browser, server, IoT device etc.). One app is running on both client and server side: this the end of the SEO pain and code duplications.
both sides: JS ;) - bundle with Browserify/Webpack - modules that runs on both sides -> npm: superagent etc. - view engine that renders on both sides: - React, - VirtualDOM...