Newton for Mac, Windows and Linux has a calendar for Google Calendar. You can see your day, add events and answer invitations without leaving your inbox. Outlook and other calendars aren't supported yet.
Steps
Open Settings: press ⌘, on Mac, or Ctrl+, on Windows and Linux.
Go to the Accounts tab and select your Gmail account.
Under Calendar, click Enable Calendar.
Sign in with Google in your browser and allow access to your calendar.
Back in Newton, click the calendar button in the toolbar at the top of the main window.
In the calendar:
Use the arrows to go to the previous or next day, or click the date to pick another day.
Click the + button (New event) to add an event. You can set a title, times, location, participants, a description and a Google Meet link under Conference.
Click an event to see its details. Answer Are you attending? with Yes, Maybe or No, or use the Edit event and Delete event buttons at the top.
Good to know
The calendar works with Gmail and Google Workspace accounts only. Outlook, Microsoft 365 and iCloud calendars aren't supported yet.
It shows your main Google calendar. Other calendars in your Google account don't appear.
If you have several Gmail accounts, turn it on for each one. When you add an event, you choose which account it goes to.
The calendar is only in Newton for Mac, Windows and Linux. The phone and tablet apps don't have one.