Wren - Offset your carbon footprint by saving rainforests
Fantastical 2 - Fantastical, the Mac calendar app you'll enjoy using. Quickly create new events with natural language input and more.
Klima - Go carbon neutral
Google Calendar - Spend less time managing your day & more time enjoying it
YAYZY - Track the carbon footprint of each purchase in real-time
Itsycal - Itsycal for Mac. Itsycal is a tiny menu bar calendar. If you want, it will display your events as a companion to the Mac Calendar app. You can also create and delete (but not edit) events. Download Itsycal for macOS 10.