Tiling window manager for OS X similar to xmonad, written in pure Objective-C.
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Pro It's free and open-source
Amethyst is published under the MIT license making it open-source and id offered completely free. This allows anyone to give the tiling window manger a try, which is great.
Pro Recently updated and rewritten in Swift.
The application was written in Objective-C, but was recently updated and completely rewritten in Apple's new native language Swift.
Pro Works with keyboard shortcuts, no mouse needed
By be designed to work closely to how xmonad works Amethyst uses keyboard shortcuts to control the windows being used with no mouse input necessary. This can make for a faster way to control windows one one gets used to using the keyboard for all window controls.
Pro Multi-monitor suppport
Con There are more user friendly window managers available.
There are certainly more user friendly window managers available for MacOS, such as Divvy or Moom. Amethyst, however, is more powerful and customizable than the more user friendly options available and therefore may be a better choice for a user looking for more advanced capabilities and customization.