Google Developer Groups (GDGs) are for developers who are interested in Google's developer technology; everything from Android (https://developer.android.com/) with Java & Kotlin (https://kotlinlang.org/), Firebase (http://firebase.google.com), Progressive Web Apps with Polymer, Angular (http://angularjs.org) web apps, Flutter, Google Cloud Platform (http://cloud.google.com), TensorFlow (http://tensorflow.org) (machine learning) and various other APIs & SDKs.
