What is the BlackBerry Hub+ Calendar application, how does it work?

According to the introduction of BlackBerry Limited, BlackBerry Hub+ Calendar is a Productivity app on the Android platform. There is currently a 2.1910.0.17488 version released on Dec 02, 2019, you can see the details below.

BlackBerry® Hub+ Calendar allows you to schedule appointments and create events with ease. Use the Agenda, Day, Week, or Month view to quickly glance at your events. The BlackBerry Hub+ Calendar lets you view and respond to meeting invitations directly from the BlackBerry® Hub+ Inbox. You can also call into meetings directly from your event reminder with just one tap.

Major Features:
• Sync work and personal accounts for a truly integrated experience. Supports Google Calendar, Outlook.com, Office 365, Microsoft Exchange ActiveSync, and subscribed calendars, amongst others
• Forward and respond to meeting invitations from BlackBerry Hub+ Calendar or Inbox quickly
• Meeting mode automatically silences your audible notifications during meetings
• Manage multiple calendars, and search for calendar events by subject, location, or participants
• Agenda view widget lets you see your schedule from your home screen at a glance
• Dark theme option gives your BlackBerry Hub+ Calendar a fresh new look and feel
• Fully supports Android Enterprise deployment and, when allowed by your administrator, supports unifying your personal and work calendars while maintaining strict data storage separation

BlackBerry Hub+ Calendar requires the BlackBerry® Hub+ Services app to deliver a consistent experience across all BlackBerry® applications, and to manage your subscriptions
Enjoy BlackBerry Hub+ Calendar for free on your BlackBerry® device!

If you don't have a BlackBerry device:
• Enjoy full functionality of the app for 30 days
• After 30 days, use the app with full functionality and some ads
• Purchase a monthly subscription to enjoy BlackBerry Hub+ Calendar without ads. This grants you access to all the BlackBerry Hub+ apps, including Inbox, Contacts, Notes, Tasks, and Launcher
• Enterprise Customers, please visit: http://web.blackberry.com/enterprise/contact-us
For support, visit docs.blackberry.com/en/apps-for-android/calendar/