As the first major release since Apple open-sourced the Swift programming language and began providing Linux support, Swift 2.2 is now available.
Swift 2.2 contains the Linux support (officially for Ubuntu 14.04 and 15.10) while aside from that are some minor language changes. Swift 2.2 is "mostly source-compatible" with Swift 2.1 and there are also a number of bug fixes, diagnostic enhancements, and performance improvements. A Swift Package Manager is also in development but not bundled with Swift 2.2.
More details on Swift 2.2 can be found via today's release announcement at Swift.org.