The PyAddressbook program is vcard based and supports the basic features of a vcard. At the moment name, address, telephone, email, birthday are supported, but more features are going to be implemented. vCards can be imported (and most programs can export vCards), but they can also be exported, to share them with other people.
The interface is built around the capabilities of a vCard, that means the meta information for a supported fields is defined in the vCard standard and at the moment no other meta information is supported.
The startup is quite fast, and the project aims to be lightweight, but still offering a good addressbook (and that's also all it will offer, so it's not planned to become a full featured PIM).