Kontact
Kontact is a personal information manager and groupware software suite developed by KDE. It supports calendars, contacts, notes, to-do lists, news, and email. It offers a number of inter-changeable graphical UIs (KMail, KAddressBook, Akregator, etc.) all built on top of a common core.
Differences between “Kontact” and “KDE PIM”
Technically speaking, Kontact only refers to a small umbrella application that unifies different stand-alone applications under one user interface. KDE PIM refers to a work group within the larger KDE project that develops the individual applications in a coordinated way.
In popular terms, however, Kontact often refers to the whole set of KDE PIM applications. These days many popular Linux distributions such as Kubuntu hide the individual applications and only place Kontact prominently.
History
The initial groupware container application was written in an afternoon by Matthias Hölzer-Klüpfel and later imported into the KDE source repository and maintained by Daniel Molkentin. This container application is essential for Kontact to operate, but without embedded components is not useful by itself.