What is the difference between Android 6 and Android 7?

In Android 7 (Nougat), the key differences from Android 6 (Marshmallow) are:

• Multi-window mode: The ability to display two applications simultaneously on the screen.
• Enhanced notifications: Grouping, the ability to reply to messages directly from notifications, expanded notifications.
• Doze mode (improved): More aggressive power saving activated when the device is stationary, even in a pocket or bag.
• Vulkan API: Support for a new graphics API to improve game and application performance.
• Direct boot: Quick access to certain functions after device restart, before entering the password.
• System updates without interruption: Installing updates in the background.
• New Quick Reply settings: Quick access to frequently used settings in the notification panel.
• Improved performance and optimization: Reduced power consumption and increased speed.
• New emojis (Unicode 9).

The main focus in Android 7 was on increasing performance, improving user experience, and saving energy.