Blockchain providers are using Java for the backend and also use clojure & node for the smaller backend systems. Its frontend is built on AngularJS and the database used is MySQL. The frameworks used by them for various platforms are:  1. Android: Junit, apache-commons, bitcoin, Gradle 2. iOS: JSBridgeWebView, storyboards 3. Web: Bootstrap, BitcoinJS, Jasmine (for tests), ES6, Travis, NodeJS, NPM, AngularJS