WordPress 4.0 beta, a major update, is officially released now for testing and can be downloaded from here. But before you download it, lets look over some key features it offers :
1. Selecting Language at the time of installation. As soon as you begin installing WordPress 4.0, you are greeted with this language selection screen
2. Previews of embedding via URLs. As soon as you paste a URL from sites like youtube.com or wordpress.tv in the visual editor, you will see a preview of the link you just posted.
3. Addition of Grid View in in the Media Library in addition to the List view.
Clicking on any media item from the list, open up a new modal where you can see a bigger preview and edit the metadata of the it. You can also edit images and scroll through the rest of the items in the list via a navigation bar on top.
4 . New interface to install and search plugins.
5. New Widgets interface.