Multimedia

Mathematics

Sage

http://www.sagemath.org/

Graphics

Inkscape: Vector Graphics Editor

http://inkscape.org/

Office

Libreoffice: Office Suite

http://www.libreoffice.org/

Google Documents: Online Office Suite and Repository

https://drive.google.com/?pli=1#

Audio and Video

Audacity: Audio Recorder and Editor

http://audacity.sourceforge.net/

Cinelerra: Video Editor and Compositor

http://cinelerra.org/

Screen and Video Capture

Shutter: Image Screen Capture Tool for Linux

http://shutter-project.org/

Greenshot: Image Screen Capture Tool for Windows

http://getgreenshot.org/

RecordMyDesktop: Video Capture Tool for Linux

http://opensourceecology.org/wiki/RecordMyDesktop