Welcome kuiserver applet, the very first applet that uses extenders in trunk.
This commit includes the kuiserver dataengine (works pretty well, but atm requires a patch to kdelibs:
see plasma/engines/kuiserver/kdelibs_kuiserver_patch.diff) the kuiserver applet (needs some love and doesn't work anymore in panel, since I'm trying to get it work nicely with popupapplet), and the extenderapplet, a simple container for extenderitems and also currently the default applet thats get created when you drop an extenderitem somewhere where there isn't an extender yet.

Have fun! :)