Apple has introduced Safari Technology Preview (https://developer.apple.com/safari/technology-preview/), a new version of its web browser aimed specifically at developers. It provides an early look at upcoming web technologies in OS X and iOS including the latest layout technologies, visual effects, and developer tools.
Safari Technology Preview is a standalone app that works side-by-side with the current version of Safari, so you can continue to use and reference the current release. It works with iCloud, so you can access your latest Safari Favorites, bookmarks, and Reading List.
You can update Safari Technology Preview right from the Mac App Store. Updates occur every few weeks and include the most recent additions and improvements to WebKit, the open source browser engine. Though it’s designed for developers, you don’t need a developer account to download Safari Technology Preview.