Memotoo sync all your contacts from Gmail, Facebook, phone, Thunderbird, Outlook, etc in a single address book.

Kolab Now is a web-based email and groupware service, based completely on free and open-source software.

The Bat! is an email program for Windows that protects the correspondence and empowers the users to handle large amounts of emails quickly and efficiently.

SugarCRM is a customer relationship management (CRM) system.

Claws Mail is a free and open-source, GTK+-based email and news client. It offers easy configuration and an abundance of features.

FullContact gives you all the power of your address book, right in your Gmail inbox.

Soocial provides a synchronization service that syncs contacts between the users' computers, phones and web apps.

Stoq is an open source framework for enterprise level automated analysis.

Kontact is a personal information manager and groupware software suite developed by KDE. It supports calendars, contacts, notes, to-do lists, news, and email.

eM Client is a Windows based e-mail client for sending and receiving e-mails, managing calendars, contacts, and tasks.

AdiInviter Pro is a contact importer and tell-a-friend platform.

Evolution is the official personal information manager for GNOME.

FCorp ID Book is a portable, light but powerful address book.