Andrew Nacin the lead developer at WordPress just announced in a blog post that WordPress 3.9 beta 1 is released for people who want to test it, and live on the edge, or bleeding edge…
You can start using this build by downloading the WordPress beta tester plugin from here
What’s new in this release:
1- Updated TinyMCE, the software powering the visual editor
2- Added widget management to live previews
3- The same 3.8′s beautiful new theme browsing experience is now in the theme installer.
4- Galleries now receive a live preview in the editor
5- You can now drag-and-drop images directly onto the editor to upload them.
6- Some things got improved around editing images.
7- New audio/video playlists.