fn (DisplayName) in CardDAVMATE
CardDAVMATE is a great web application to edit contacts in a carddav server licensed unter the GNU Affero General Public License (version 3.0). You can find the software at https://www.inf-it.com/open-source/clients/carddavmate/.
One of the details I personally lacked is the possibility to view and edit the "fn"-attribute (also known as displayname). I had a short conversation with Ján Máté where he explained that his opinion is that this field is redundant and therefore should not be available as a separate field.
In my opinion, CardDAVMATE is a UI to an existing database and it was decided to have the displayname as a separate field. Regardless of this being a good or a bad decition (which I don't want to elaborate on!), making the UI different to the database design can cause inconsistency with other UIs.
Therefore, I created a patch to have the displayname available in CardDAVMATE. The main limitation is the localization. The only real localization implemented is German, all other languages default to English. If you want to provide additional localizations, feel free to contact me.