Internet

Collaborative tools 

Etherpad

Etherpad (former EtherPad) is a web application text editor, it is a real-time collaborative tool that permits edit a text document simultaneously (and display each entry user in a different color; it includes a chat box for the communication between the related users).

Launched in 2008, it was acquired by Google in 2009 and released as open source later (the development is coordinated by the Etherpad Foundation).
Several services now use this software, such as TitanPad, PiratePad, board.net, Mozilla Pad (MoPad), PrimaryPad, etc.

  Image source: Etherpad" by Gegensystem - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons
 

URL:  http://etherpad.org/

Version for internet browsers.
Licenses under Apache License 2. (compatible with GPL v3.0.)

Graphic Apps

GIMP (GNU Image Manipulation Program)

GIMP is a free and open-source graphics editor used for editing and manipulating raster (raw and non vectorial) images (free-form drawing, resizing, cropping, photo-montages, converting between different image formats and more funcionalities depending on plugins).

URL:  www.gimp.org

Version for GNU/Linux, OS X, Microsoft Windows, FreeBSD, OpenBSD, Solaris, AmigaOS 4
Licenses under LGPLv3 and GPLv3+.