Microsoft is testing some privacy and notification features in its latest Windows 10 Insider preview for Fast Ring users. A previous build added an icon to the notification area that tells you when your microphone is in use, and the newest update will let you see which app is using it when you mouse over the icon. If more than one app is using your mic, the icon will tell you how many. It's a useful privacy enhancement, especially if you're concerned about eavesdropping.
After making it easier for you to pause updates in the last preview build, Microsoft has added an orange indicator to the system tray to let you know when you have an update waiting that requires a reboot when you install it. That should help you avoid having to restart your system when you're not expecting to.
Microsoft is also tweaking the design of the Start power and user menus, and adding an option to manually sync your clock with the time server. It's adjusting Search and Cortana as well, so that the recent activities section of the landing page has "a bit more room to breathe," while it's adding support for a light theme. The company has also added an option to switch directly to your To-Do tasks in the Mail and Calendar app for both testers and general users.