Please read the paragraph on currently known issues. We currently support ONLY MacOS (Yosemite, El Capitan and newer). In principle, however, it should work analogously with all CalDAV and CardDAV clients. Either as easy as with MacOS (e.g. KDE Calendar) or a bit more "bumpy" (e.g. Evolution, Thunderbird-Lightning). How you can find out your CalDAV/CardDAV paths is shown below.
Calendar
Create a new CalDAV account in the Mac calendar with Add calendar account.
Select the automatic configuration with your e-mail address (....@oth-aw.de) and password. Alternatively, you can also select the manual configuration with the server: "xdav.oth-aw.de", your CC account with password.
Contacts
Create a new CardDAV account in Mac Contacts with Add Contacts Account (you need to scroll all the way down).
Select the automatic configuration with your e-mail address (....@oth-aw.de) and password. Alternatively, you can also select the manual configuration with the server: "xdav.oth-aw.de", your CC account with password.