Kate and other editors use the katepart editor component
Several applications use the Konsole KPart to embed a terminal
Solid
Solid is a device integration framework for KDE Platform 4 and its successor, KDE Frameworks. It functions on similar principles to KDE's multimedia pillar Phonon; rather than managing hardware on its own, it makes existing solutions accessible through a single API. The current solution uses udev, NetworkManager and BlueZ (the official Linux Bluetooth stack). However, any and all parts can be replaced without breaking the application, making applications using Solid extremely flexible and portable.[5][6] Work is underway to build a Solid backend for the Windows port of KDE based on Windows Management Instrumentation.[7]