Having settled on Mailspring to deal with my email, I needed a separate Calendar app. There are several to choose from and both California and Gnome Calendar meet most of my needs.
Both apps link flawlessly with my Google Calendar and appear to sync both ways without issues. Neither recognise Google tasks however. Both provide an attractive uncluttered interface and whilst Gnome Calendar allows the setting of alarms / reminders for calendar events, California offers an Agenda view as well as week and month views. The Gnome calendar is obviously themed for the Gnome desktop.I like them both!
Above: Gnome Calendar.