Dexter is described as 'very simple, easy to use address book, designed with the' and is a Contact Manager in the Office & Productivity category. There are six alternatives to Dexter for Windows, Linux and GNOME. The best alternative is Kontact, which is both free and Open Source. Other great apps like Dexter are GNOME Contacts (Free, Open Source), Kontact - KAddressBook (Free, Open Source), E-Z Contact Book (Freemium) and Contacts Express (Free).
Kontact is the integrated Personal Information Manager of KDE. Kontact suite unites mature and proven KDE PIM applications under one roof. Thanks to the powerful KPart technology, existing applications are seamlessly integrated into one.
Contacts keeps and organize your contacts information. You can create, edit, delete and link together pieces of information about your contacts. Contacts aggregates the details from all your sources providing a centralized place for managing your contacts.
It supports large variety of services, including NextCloud, Kolab, Google Contacts, Microsoft Exchange (EWS) or any standard CalDAV server. Features: Powerful search - KAddressBook has configurable filters and powerful search capabilities.
E-Z Contact Book is a free easy to use yet powerful Windows program to store and manage contact information. You can use it as a business directory, customer database, or a personal contact address/phone book.