Windows 10 build 10074

Windows 10 build 10074 is the first officially released Insider Preview build of Windows 10. It was released to Insiders on April 29, 2015. This build contains the new flat icons.

Cortana

 * Start and Cortana are now more tightly integrated.
 * New experiences in Cortana powered by Bing Instant Answers.

Music and Video Preview Apps

 * Music app is more immersive with a true full screen mode.
 * You can download movies, TV shows and TV seasons with the Video Preview app on up to three devices.

Other

 * Closing an application in Tablet Mode takes you to the Start screen now.
 * Multi-tasking improvements - Alt+Tab, Task-View, Snap Assist.
 * Windows Store has been expanded to 41 more markets.
 * Windows Store is now a blue tile instead of gray.
 * New system sounds added, however they were changed to the RTM sounds at a later date.