Can I code using Swift on Mavericks?
To code using Swift you'll need Xcode 6. 

Xcode 6 beta is compatible with Mavericks 10.9.3 and upwards so yes it is possible to write Swift code in Mavericks!

NB: As of July 11, Xcode 6 beta is available freely on Apple's website.


Where can I download Xcode (n) Beta?