I know that lots of the people choose to use open source software for their productive purposes. Linux is a vast ocean of open source apps. It’s easy to get lost in this ocean, and is even hard to find out about some great applications that are out there.
Thus, I hope that this modest list will help someone to discover a new application that they will love.
Inkscape
An Open Source vector graphics editor, with capabilities similar to Illustrator, CorelDraw, or Xara X, using the W3C standard Scalable Vector Graphics (SVG) file format.

Cenon
Cenon is another great graphical tool for vector design and desktop publishing.

Endeavour Mark II
Endeavour Mark II is a complete file management suite that comes with a file browser, image browser, archiver, recycled objects system, and a set of file and disk management utility programs.

Gcolor2
Gcolor2 is a simple color picker.

gParted
The GParted application is a graphical partition editor for creating, reorganizing, and deleting disk partitions.

Cinefx
Cinefx is a suite of open source, cross platform media playback, encoding, visual effects and editing digital content creation tools.

KoverArtist
KoverArtist is a program for the fast creation of covers for cd/dvd cases and boxes. The main idea behind it is to be able to create decent looking covers with some mouse clicks.

Krita
Krita is a creative sketching and painting application based on KOffice technology. Whether you want to create art paintings, cartoons, concept art or textures, Krita supports most graphics tablets out of the box.

WhiteDune
White Dune is a low level VRML tool that can read VRML files, display and let the user change the scenegraph and fields.

Wings3D
Wings 3D is a free, open source, subdivision modeler inspired by Nendo and Mirai from Izware. Wings 3D can be used to model and texture low to mid-range polygon models.

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Interesting list, but this post might’ve been a bit better if you’d added a short summary of what each application does. Even if it just said “video editing”, “3D graphic design”, etc.
Finally a list without the contrived VLC, Compiz, Amarok crap. Something original so users might actually put something else on their systems to see what it can do. Good job
Awesome list… It’s nice to see somebody boast some applications that don’t come pre-installed on Ubuntu.