WordPress 4.4 Beta 1 is available. The release snuck up on me, as it feels like a long time from the expected December release. Maybe it's just the whole year that's flying by.
4.4 includes lots of great developer features, plus Twenty Sixteen, responsive images, and embeds. The biggest features by far, for my audience, are phase 1 of the REST API, responsive images, and term meta. The links there are to podcasts where we talked about these new features, or search the site for many links to various discussions of these new features.
I love WordPress 4.4 already. I've been using it a good bit in development, and it's awesome. Check out the release post and test it out. There's still plenty of work to do. Expect new beta releases and RCs for the next five to seven weeks.