What is "swift-3"

Swift is a programming language for applications and systems introduced by Apple on June 2, 2014, and distributed as open source. Swift interacts with Objective-C and Cocoa / Cocoa-touch Apis for Apple’s OSX, iOS, tvOS and watchOS operating systems.

Current and stable version of Swift is Swift 3.1 released and made available on 27 March 2017. Release Notes.

Swift now is open source, available on Github
Swift >= 2.2 includes support for Swift for Linux platform.
The development of Swift 4.0 is underway with priorities, including ABI stability and improvements for reflection, among others.

Swift promises to modernize the developer experience of what Objective-C offers, offering features such as:

Error handling Type of security Type inference Namespaces Increased security (some overflow protection, use before startup, etc.) Higher order functions (map, filter, sort) among others.

Swift syntax retains some elements of Objective-C, providing an extensive new vocabulary for its new features.

The language can use existing iOS and OSX frameworks, such as Cocoa and Cocoa-Touch, and can sit side by side with Objective-C in apps. Swift applications compile in standard binaries and can run on OSX 10.9, iOS 7 (or higher), tvOS and watchOS.

Timeline:

Swift 2.0 was introduced by Apple to the WWDC on June 8, 2015. They added new features like the "Bug Handling Model" with try, throw and catch.

Swift 3.0 was introduced by Apple in the WWDC on June 13, 2016, with the news of Swift will reach all platforms (macOS, Windows, Linux, Android, Raspberrypi, and so on ...)