In my opinion the best feature of the WordPress 4.4 released today (8 December 2015) is builtin support for responsive images. Upload your images and WordPress 4.4 does the rest! Now your images will look great on all devices: desktop, tablets, and smartphones.
Also included in this version is a new theme. The theme is a classic blog design built on a fluid grid design. There is a flexible header and several color schemes, although you can select any color you want to use through the Customizer.
WordPress 4.4 also has included more oEmbed functionality letting you embed content from Cloudup, Reddit Comments, ReverbNation, Speaker Deck, and VideoPress. Even better you can embed any WordPress post within your page or post like what is displayed below. It will include the featured image, if specified, the site icon and share information.
For those interested in what changed “under the hood,” you can get the full details here:
The addition of the REST API has made the biggest news among developers. It should make for some interesting and exciting functionality to themes and plugins in the months to come.