I just released a first (beta) version of CalCleaner, a small tool to cleanup CalDAV calendars. The software has a GTK 3 graphical interface and is currently available on Linux.
The interface is quite simple. At the first start, the application offers you to connect to a calendar server (thereafter it is possible to add, delete and modify accounts via the application menu).
The next view shows us the list of calendars accessible with the configured CalDAV account(s). It is then possible to uncheck the calendars that you do not want to process (I personally do not want to clean the birthday calendar 😛️). It is also on this screen that you can define the age of the events to be deleted and whether or not to process recurring events...
Once you are ready, just hit the "Clean Now!" button and CalCleaner will start its work. 🗓️🧹️