Install Swift 3: macOS
To use Swift 3 on macOS, you just need to have Xcode 8 installed.
Install Xcode 8 from the Mac App Store.
After Xcode 8 has been downloaded, you must open it to finish the installation. This may take a while.
Double check the installation was successful by running:
curl -sL check.vapor.sh | bash
You can now move on to Install Toolbox.
Check out Swift.org's extensive guides if you need more detailed instructions for installing Swift 3.0.