Joomla 3.8 stable version is around the corner, now you may download the Joomla! 3.8 Beta release for testing that's why DO NOT use the beta version on your live production website since it's still not ready and needs the final fixes and improvements before the official Joomla 3.8 stable release.
Moreover, note that the beta release cannot be upgraded which means that you there will not be an upgrade path from the beta to next higher ones. All community members who find bugs in Joomla 3.8 beta may report issues in the Joomla! CMS Issue Tracker.
Joomla 3.8 developers assure template and extensions providers that there shouldn't be any backward compatibility issues. However, we will also do tests with all our Joomla products to make sure if Joomla templates or extensions updates are needed to use Joomla 3.8. After testing we will inform our customers about new Joomla 3.8 templates version via newsletter.
The stable Joomla 3.8 is planned to be released on 19th September 2017 and it's not the fixed date - it may change.
New routing system improves managing URL structure also taking into account the often requested issue by Joomla users to remove IDs from URLs.
Joomla! 4 compatibility layer implementation for Joomla 3.8 code structure to help developers on their work on the extensions integration with the new layout. It should simplify Joomla developers work on preparing extensions for Joomla 4 at the same time.
Improved sample data installation gives the possibility to install sample data for Joomla extensions after installing Joomla CMS. It is a big and valuable improvement for Joomla developers and can't wait to check how it works in detail. The sample data installation is handled with the back-end module and plugins. Available sample data to will be displayed in the administrator panel and ready to install.
In a similar way to the default built in Joomla sampledata may be created by Joomla extensions providers to let creating the sample data for the specific component or template
and install it showing info about the sample data installation progress.
Sodium encryption support by adding a new API available for all of our users who want to use the new sodium extension for processing encrypted data (even before updating to PHP 7.2)L
Accessibility improvements in Joomla core views for better readability for screen readers. Joomla developers have improved the read more links, page navigation, and article tool icons. These improvements result in better compatibility with the WCAG 2.0 and Section 508 standards in Joomla 3.8.
For more improvements look on the Joomla 3.8 tracker -> https://github.com/joomla/joomla-cms/milestone/19 where you may control progress for still open issues.