via Apple Kbase:
Other improvements
• New San Francisco system font
• Leave a message option if recipient isn’t available for a FaceTime call
• Share voicemails from the Phone app using the share sheet
• Flight and package tracking for data detectors
• Health app adds support for reproductive health, UV exposure, water intake and sedentary state data types
• HomeKit adds support for motorized windows and shades, motion sensors and home security system accessories
• Podcasts has an all-new design, makes it easy to find the latest episodes of your favorite shows and notifies you when new episodes become available for you
• Support for Wi-Fi calling on iPad, iPod touch and Mac, without iPhone in proximity on participating carriers
• Wi-Fi Assist to automatically use cellular data when Wi-Fi connectivity is poor
1400 word KBase document outlining the hundreds of iOS 9 changes. Check it out.