When comparing Amethyst vs GameGuru, the Slant community recommends Amethyst for most people. In the question“What are the best 3D game engines?” Amethyst is ranked 26th while GameGuru is ranked 38th. The most important reason people chose Amethyst is:
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.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

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
As it's designed to work closely to how xmonad, Amethyst uses keyboard shortcuts to control the windows being used, meaning no mouse input is necessary. This can make for a faster way to control windows.
Pro Multi-monitor suppport
Pro Has many common layouts to choose from (fullscreen, floating, row, column, wide, etc)
Pro Can switch between tiling and floating mode
Pro Under active development
Pro Configured via UI
No CONFIG file provides security and will avoid making amethyst crash. Instead configured via simple UI
Pro True tiling means never losing track of windows under a huge pile of others

Pro Designed for ease of use
Simplicity and accessibility are the core design goals of FPS Creator Reloaded.


Pro Active and helpful community
Users share ideas, help, and advice through the official forums. The community also provides a wealth of free assets, and the GameGuru Assets Store sees constant additions.

Pro Continuous development and updates
News and improvements are released on a monthly schedule. Interaction between The Game Creators and project backers is excellent.


Pro Awesome tech support

Pro Easy to use your own custom assets
Easily import your own 3D models with the built-in importer and create custom characters with the Character creator. Custom weapons are much more difficult, though.
Pro Massive community of users
The gamer creator forums have a large number of users, developing games, making models for sale and to give away for other users. They answer questions, help each other with problems in their games, and can make using this software so much more fun and easy.
Pro Royalty free
Games you publish with GameGuru can be sold without any restrictions or commissions.
Pro Easy to use editor
An easy 3D editor to create your own maps in seconds with drag-and-drop function.

Pro Friendly GUI
Awesome friendly GUI, and quite easy to use.
Pro Building editor
Currently in development but already looking very good! Easily create big and customized buildings with default building blocks and share them with others.
Also very easy to use in the designer: The buildings are treated like entities but still directly available in the 'building editor mode'.
Pro Powerful scripting language
Uses Lua.
Pro Large asset store
A store where you can buy various assets for your games like sounds, 3D models, weapons... Very good prices and a lot of assets are even free.

Pro Feature priorities are chosen by the community
The Game Creators team frequent the forums and ask the community for feeback and suggestions both there and via an open poll on the website. They have a great history of reading suggestions, viewing screenshots, and generally working with the community.
Pro Optimised engine for editor
The game engine is optimized for efficient use of memory.
Cons
Con Can be buggy at times
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.
Con Slow
Everything takes ages..feels like Unreal 4
Con Lack of user-interface
Although you can customize a lot, the user-interface does not show that. But plans are in place to improve this with some front facing GUI into the LUA scripts so you don't need to code as much.
