KDE PIM is an application suite for KDE SC that helps you to organize your mail, addresses, todo's, appointments, and so on. Beyond this, it keeps your mobile phone and PDA in-sync with your desktop data.
Development of KDE PIM applications takes place mostly in KDE SVN but it is migrating to KDE git. Together, the applications are about 74MB of source -- a daunting amount. These developers webpages are meant to give you a place to start, to collect documentation and explain how development within KDE PIM works.