org-gnome-calendar

Provides the global minor mode `global-org-gnome-calendar-mode' to export the
entries in the Org mode agenda to GNOME's calendar menu.

If you also want to show an Org mode agenda when clicking into "Open
calendar" in GNOME's drop-down calendar menu, you can use "dconf-editor" to
set path "org.gnome.desktop.default-applications.office.calendar" into:

  emacs --eval '(progn (org-agenda nil "a" nil) (delete-other-windows))'