Develop a A) WordPress backend to add and edit entries inside a database table. These entries include a title (string) and occurrence information like "21. January" or "Third Tuesday in January".
Besides this backend administration panel, the plugin should B) also provide functionality to make this events accessible as iCal URL calendar stream (e.g. [login to view URL]). This to make it possible to calendar applications (iCal, Fantastical, Google Calendar, Outlook etc.) to subscribe to this calendar and see the entries as "full-day events".