Free, open-source alternatives to Fantastical

Fantastical is a calendar app that is reachable from the menu bar and lets you add events by typing a sentence. The open-source apps below share its menu bar calendar: a month view one click away that shows events from the calendars already set up on your Mac.

Calendr is the closer match, with natural-language entry for new events and extra time zones in the menu bar. Itsycal is a smaller menu bar calendar focused on a quick look at dates and upcoming events. Both read the calendars macOS already knows about rather than connecting to services themselves.