Swift's evolution

Swift started out as a general-purpose programming language, intended to replace Objective-C as the default language for building iOS, tvOS, watchOS, and macOS applications. Swift is a compiled language that compiles down to Low Level Virtual Machine (LLVM) bytecode and is Just-In-Time (JIT) compiled to native code of the architecture on its first run making Swift a very fast language. Swift also uses Automatic Reference Counting (ARC) to manage memory, making it simple to write applications especially for iOS where memory management is critical.

With all of these features, Swift definitely stands out from the rest of the languages popular during that time, which included Scala, Rust, Elixir, Kotlin, and C#. With growing popularity, all it needed was more platforms to run on and that is what Apple did when they open sourced it in late 2015.