Typically, iOS developers for hire are like universal soldiers: they can work with standardized languages, APIs, frameworks, and architecture. The whole iOS development paradigm is based around Swift, also known as a proprietary programming language created by Apple. In general, good iOS developers for hire should be proficient in: Swift, Objective-C; OOP, SOLID principles; iOS SDK, UIKit, CoreData, APNS, Apple Purchasing, GeoLocation Service, Networking, Multithreading; GIT version control system.