Android: SDK, Services, Fragments, Broadcast receivers, Content providers, Custom UI components, GPS, Sensors, Localization, Tablet adaptation, Build flavours, ProGuard, etc.
Core Technologies: SQLite, RESTful API, HTTP, SSL, Websockets, HTML, XML, JSON.
Third Party SDKs and libs: Facebook, Twitter, Google+, VK, Instagram, Foursquare, Google Analitycs, Google Maps, Google Places, Picasso, Android Annotations, okHttp, Retrofit, JavaRX, Stripe, External GUI libs, etc.
Build Tools: Gradle, Maven.
IDE: Android Studio, IDEA.
VCS: Git, SVN.
Tracking Systems: Jira.
OS: Windows, Ubuntu.
Methodologies: Scrum, Kanban
Other: Design patterns, UI Guidelines.