Cantata is a graphical front-end for the music player daemon, MPD. It provides many tools to view and manage the music collection including:

KWordQuiz is a general purpose flashcard program, typically used for vocabulary training.

OpenShot Video Editor is a free, open-source, non-linear video editor. It can create and edit videos and movies using many popular video, audio, and image formats. Create videos for YouTube, Flickr, Vimeo, Metacafe, iPod, Xbox, and many more common formats!

Brewtarget is a calculator for brewing beer. It is a Qt-based program which allows you to create recipes from a database of ingredients. It calculates all the important parameters, helps you with mash temperatures, and just makes the process of recipe formulation much easier.

Avahi is a fully LGPL framework for Multicast DNS Service Discovery. It allows programs to publish and discover services and hosts running on a local network with no specific configuration. For example you can plug into a network and instantly find printers to print to, files to look at and people to talk to.