There’s a lot about vCards in Roundcube. No surprise, this is simple and established open standard. Contacts import and export is based on it, as well as Roundcube’s internal format for contacts. There’s also the vcard_attachments plugin that adds some more functionality around vCard use.
As the plugin name suggests it’s about handling of vCards in attachments. So, if anyone sends you an attachment which is a vCard you can add it to your address book with one click. This functionality you might already know as it’s there for a long time.
Recently added feature allows you to send such attachments. So, in compose window, you can select a contact and attach it as a vCard to the message.