Multimedia

There are distributions dedicated to multimedia production, such as Ubuntu Studio. Some of the most known apps are:

GIMP: full feature image editor, comparable to Photoshop.
Inkspace: dedicated to the creation of vector images (.SVG).
Audacity: audio editor (wav, mp3, ogg, etc.)
Blender: create or model 3D animations.
VLC: video playback
ImageMagik: modify and convert many image or pdf file format. Batch conversions.