- UI : Material design, Material animations, Custom components, User Interaction(touches, gestures) - Core : Intents, Services, Receivers, Content Providers, Multithreading, Dependency injection(Dagger, Butterknife), Rx Java, Job Queue, - Communication & Networking : HTTP, REST, OkHttp, Retrofit,Gson, Jackson, UIL, Parse.com, Volley, Socket, JSON, XML, SMS, Bluetooth, NFC - Build: Gradle, Maven, - Testing: Unit Tests, Android Tests, Espresso, UIAutomator - Hardware and Media: GPS, Playing Audio/Video, Accelerometer, Camera - Persisting Data: SharedPreferences, Files, SQLite, Backup and Sharing data - Interacting with System: Notifications, Alarm Manager, Timed and Periodic Tasks, Persistent Background Operations, Contacts, Calendar - Graphics: Canvas - Social: Facebook, Twitter, Linkedin, Instagram, Google+ - Google Services: Firebase, Analytics, Maps, Location, Cloud Messaging, Mobile Ads, - Vcs: Git, Bitbucket