The new WordPress 4.1 beta is out. You can participate in giving feedback before it’s officially released next month.
WordPress 4.1 adds several new features, including a new theme called Twenty-Fifteen, being able to automatically install new language packages from the general setting screen, a new distraction free mode, along many others.
WordPress 4.1 is available for beta testing with the WordPress Beta Tester Plugin.
When testing the beta, if you find any bugs, you can contribute by reporting it to the Alpha/Beta support forum.