Gathering software requirements using interviews, documents analysis, use Database architect (Data schema, EER notation), BDD, TDD, UML 2.0, REST, Google Cloud,Office 365, Eclipse, NetBeans, IntelliJ IDEA, Android Studio, Java, Kotlin, Swift, JSP, Servlets, JDBC, Oracle, SQLite, EJB, Hibernate, Apache Tomcat, Apache Maven,Json, XML, Apache Ant, Gradle, Jenkins , VOIP, SIP,RTCP, XMPP, WebSocket, Web RTC, Dagger 1, Dagger 2, ORM lite, Material designe, Google support libraries, GreenDAO, SQLBrite, RxJava, RxAndroid, RxKotlin, Mockito, JUnit 4, Spec, Kotlin test, Google GSM, AIDL, QuickBlox SDK, Custom photo\video camera implementation, lib stream (video streaming), iBeacon, Android architecture best practices, Picasso, ButterKnife, Glide, Retrofit 1, Retrofit 2, Hockey app, Fresco, OkHtpp 2, OkHttp 3, Crashlytics, Conductor, Flow, GSON.