dcop is KDE's access-to-everything tool, which most KDE apps export some sort of interface to. For example, to ask the KWeatherService the current temperature in Canberra (which has station code 'YSCB'):
[jk@b4 jk]$ dcop KWeatherService WeatherService temperature YSCB 12°C
or to get the currently playing track from noatun:
[jk@b4 jk]$ dcop noatun-8897 Noatun title [The Aphex Twin] - Polynomial-C
or make kmail check for new mail:
[jk@b4 jk]$ dcop kontact KMailIface checkMail
Handy for scripting!