Free upgrade to Windows 10 for the first year for Windows 8.1, Windows Phone 8.1 and Windows 7 devices. Huge!!
Cortana comes to all Windows 10 devices and has learned new 7 languages. Hey Cortana demo also going on.
Windows 10 for phones and tablets less than 8-inch:
Action center enhanced
Skype integrated to messaging
Voice to text typing
Reading mode, reading list and support for widest range of content