Update at https://en.wikipedia.org/w/index.php?title=Comparison_of_CalDAV_and_CardDAV_implementations#Client_implementations the line about KOrganiser,KAddressbook,Kontact. Possibly add KMail, if this is how iTIP/iMIP messages arrive over mail.
It's a wiki, feel free to edit the page.
I do not use KDE, I don’t know what to write there and you do not list the supported RFC. It is up to the developers to fill the information there, as it is pretty technical for mortals.