Contacts

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Contact management is made easy by this component. You can import your contact list from nearly every application that exists, plus if you are on any network that supports LDAP, you can import contacts from the server as well. You can assign categories to your contacts. Default categories are Business, Customer, Family, Friend and School, but by clicking on “Edit categories” you can add more categories.
In addition, setting your contacts' birthdays and anniversaries make them appear in the Summary View.
Contacts module integrates with KDE’s instant messaging application Kopete like Evolution integrates with Pidgin (formerly Gaim). So, if you can gather all your contacts with all the details in Contacts, then you will have no problem working with them, be it sending instant messages or applying mail merge within KWord.
Calendar
Calendar is more than an digital agenda application. It has lots of features that Microsoft Outlook –yes, again- has yet to implement.
The basic features that you want from a calendar application such as differentiating the entries by category (business, leisure etc.) and displaying them with different colors, day/week/month views, recurring appointments etc. To make our lives easier, you can manage your calendar by dragging and dropping e-mails or attachments to create events.
Calendar can work with multiple calendars, and offers importing as well. For example, you can export your Microsoft Outlook calendar and import it to Kontact and then configure it to work with Gmail calendar. Just for a note, for the time being, Google Calendar does not support two-way synchronization, meaning that any changes in Kontact will not be reflected to the Google Calendar and vice versa.
To-do

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Another wonderful component of Kontact. To-do is your basic task management application with the first look. But this can be deceiving because what you have under the hood can not be matched with many other popular programs. First, you can create nested tasks. With this, you can see what portion of the task you have created by checking out the sub tasks.