1) Clean Code
2) Scalable Applications
3) Local Data Storage
4) Server Calls: JSON, REST, Sockets
5) Geolocation Services: CoreLocation, Mapbox, GoogleMaps
6) Firebase Services: Authentication, Database, Storage, Cloud Messaging, Crashlytics
7) Push Notifications: FCM, OneSignal
8) Social Networks Integration: Facebook, Twitter, Instagram
9) Bug Fixing