The Swift open source programming language.

Swift is a general-purpose, multi-paradigm, compiled programming language developed by Apple Inc for iOS, macOS, watchOS, tvOS, and Linux. Swift is designed to work with Apple's Cocoa and Cocoa Touch frameworks and the large body of extant Objective-C (ObjC) code written for Apple products. It is built with the open source LLVM compiler framework and has been included in Xcode since version 6. On platforms other than Linux, it uses the Objective-C runtime library which allows C, Objective-C, C++ and Swift code to run within one program.

On December 3, 2015, the Swift language, supporting libraries, debugger, and package manager were published under the Apache 2.0 license with a Runtime Library Exception, andSwift.orgwas created to host the project. The source code is hosted on GitHub where it is easy for anyone to get the code, build it themselves, and even create pull requests to contribute code back to the project.

Swift can be compiled, run in a interactive environment called a 'playground' or run as a script on computers with Swift installed.

Swift Site
Online Swift playground