The summary view provides a quick view of the current or coming events, birthdays and anniversaries. Furthermore it provides information about the weather and can include news sources as hyperlinks.
The KMail application
The KAddressBook application
The KOrganizer application
The KNode application
This part for editing notes was written for Kontact to provide an more integrated behaviour.
In the configuration dialog (accessable via Settings -> Configure Kontact) you can enable/disable the single Kontact-Plugins.