Unlike Android, Apple's iOS is a proprietary mobile operating system that can only be installed on iPhone, iPad, and other Apple mobile devices. However, it offers developers several open-source libraries, resources, and components.

Its free software development kit (SDK) gives developers access to various functions and services of iOS devices. It also features an iPhone simulator that allows app developers to recreate the appearance and feel of the device on their computers when developing an app. The iOS SDK helps developers create iOS apps with officially supported programming languages, including Swift and Objective-C. However, you can also use other programming languages to develop native iOS applications.

Due to the ownership of its ecosystem, iOS is one of the most secure operating systems. Simply put, other companies or developers can't fully access the source code. Additionally, all Apple components, especially open-source ones, are regularly checked for compliance with security requirements. This is one of the reasons developers often struggle to meet Apple's requirements when placing their apps in the Apple store. If something seems suspicious, Apple reserves the right to block apps immediately.