Syncevolution can be used to synchronize Horde Groupware data with your local computer, such as your calendar. The configuration is rather complex, even though there are a couple of good tutorials available (Horde-specific, here and here). However I still had to fumble with the settings to get it right. Here is my setup:
This is a companion discussion topic for the original entry at https://www.xltoolbox.net/blog/2015/04/synchronize-horde-calendar-with-ubuntu-using-syncevolution.html