One Calendar is an API that wraps around commonly used calendars, such as Google Calendar and Microsoft Exchange, and was developed by the team behind the One Diary app.

The new toggle essentially lets you control whether Google Calendar shares your event data with other apps on your device (the ones tapping into the Calendar Provider API).

When you give an app calendar permissions it can tap into Android’s Calendar Provider API to access schedule data that’s synced with your device. That could come from anything like Samsung ...

The Calendar API now supports push notifications - alerts sent directly to devices and apps instead of waiting for a client-side sync, a la Gmail - for updates that are practically instantaneous.

Now with support from Calendar on the web, Reminders are across most of Google’s core organization apps. Perhaps Gmail itself — and not just Inbox — is next.