Different Calendars with color code
All in one calendar and also able to Sync with any Cloud or other accounts. Not only Google Gmail Calendar
For example: you have one for work and one for private and want to have overview in this one
Or you need to add some other people's calendar, e.g. family member or college to exchange shifts/take turn for vacations and cover each other.
AdminAppiens (Developer, Appiens) commented
The app unites calendars from all your Google accounts that have been added to your device.