✔️ Sync all your past and future events with Google Calendar (just add your Google account under "Settings > Accounts" instead of syncing via the Android calendar).
✔️ Sync calendars with Google Calendar, Microsoft Exchange, CalDAV and iCloud (via the Android calendar).
✔️ Sync tasks with Google Calendar, Microsoft Exchange, CalDAV and iCloud.
✔️ Attach photos and files to your events (when syncing directly with Google Calendar).
✔️ Attach Evernote notes to events.
✔️ Weather forecast ("Settings > Weather").
✔️ Add icons to Google events (you have to add your Google account under "Settings > Accounts", then you can configure the icons under "Settings > Icons").
✔️ Five types of calendar views (day, week, month, agenda and year).
✔️ Four styles of agenda views ("Settings > Display and Use > Agenda view")
✔️ Use drag&drop to move and copy your events.
✔️ Widgets to see your events on your home screen (day, week, month, agenda, year and task widget).
✔️ Share calendars with other people (using Google Calendar).
✔️ Search function
✔️ Various reminder functions
✔️ Birthdays and anniversaries of your contacts
✔️ Floating events and completable events
✔️ Templates for events
✔️ Print to PDF function
✔️ Android Wear support (complication and agenda view)
✔️ Tasks in events (add a short list of tasks into an event)
✔️ Contacts can be linked to events
✔️ Use keywords to change the color or icons of your events ("Settings > Display and Use > General > Keywords").
✔️ Dark theme and light theme ("Settings > Design")
✔️ Many configuration options can be found under "Settings > Display and Use".
For more details please see here:
Additionally you can add ideas or vote for ideas on https://calengoo.de/features/calengooandroid
If you have problems just contact the support: http://android.calengoo.com/support