Safari Technology Preview is a Mac utility that lets you take a glimpse at upcoming Safari features. You can use this program to test some of Safari's impending attributes, such as visual effects, developer utilities, layout technologies, and many others.
The app's interface looks a lot like the main windows of the Safari program. The notable difference is located in the main menu of the utility: an additional button - Develop. By clicking over this button you will display a list showing all of the upcoming Safari features.
You will get access to experimental features (link preload, CSS Spring animations, WebGL 2.0, etc.), a timeline recording tool, an option to empty cache, and many others. In my testing, the app worked flawlessly as it completed any given task without slowing down my Mac.
My only issue with this program is the fact that it's compatible with only 2 OS X versions: Sierra (the latest stable version) and High Sierra (is currently in Beta stage).
Still, if you're a developer who works with Safari a lot, is definitely a good idea to install this app on your Mac and test its upcoming features. Plus, you don't have to pay a buck to use it on your computer.