Jmol is a Free, Open Source molecule viewer and editor. It is a collaboratively developed visualization and measurement tool for chemical scientists. Jmol is an active project, and there are new features being added to it on a daily basis. Users are encouraged to modify it to fit their needs and to contribute their changes to the project.
QCad is a powerful but easy to use 2D CAD program for Linux, Windows, and Mac OS X. It uses DXF as its standard file format. While other CAD packages are often rather complicated to use, QCad tries to stay comfortable, and even an absolute beginner can create professional drawings with a minimum of effort.
XaoS is a fast, portable, real-time, and interactive fractal zoomer. It displays the Mandelbrot set (among other escape time fractals) and allows you zoom smoothly into the fractal. Various coloring modes are provided for both the points inside and outside the selected set. In addition, switching between Julia and Mandelbrot fractal types and on-the-fly plane switching is provided.
Tux Paint is a simple and entertaining drawing program geared towards young children. It has a simple interface, sound effects, and a cartoon character (Tux, the Linux penguin). Along with drawing brush strokes, lines and shapes, you can also enter text and place "rubber stamp" (or "sticker") images on the picture. Tux Paint is extensible, and could be useful in an educational environment (such as a grammar, elementary, or grade school). It's portable across numerous platforms, and runs well even on slower systems like the Pentium 133MHz.
LiVES is a simple to use yet powerful video effects, editing, conversion, and playback system aimed at the digital video artist and VJ. It runs under Linux, BSD, Mac OS X/Darwin, IRIX, and openMosix. It is frame and sample accurate, can handle almost all types of video, and is fully extendable through plugins and the included plugin builder tool. It can also be controlled remotely using OSC.
XdTV is a program to watch, record, and stream TV. It interacts with AleVT (Teletext) and Nxtvepg (NextView) and supports the bttv, bktr, and dvb APIs. It contains some deinterlacing filters and records video files with various containers (AVI, MPEG, Ogg, etc.) and many codecs: FFMpeg >=0.4.6, XviD 0.9 and 1.x, DivX 4 and 5, and Vorbis/Theora >=1.0a5. It has some plugin capabilities.
gtkpod is a platform independent GUI for Apple's iPod using GTK2. It allows you to import your existing iTunes database, to add songs, podcasts, video, and cover art, and to edit ID3 tags. gtkpod also features international charset support for ID3 tags, detects when adding already existing songs, displays and manages the photo database, and more.
Qsynth is a GUI front-end application for Fluidsynth. Fluidsynth is a command-line software synthesizer based on the Soundfont specification. Qsynth was built with the Qt4 toolkit using Qt Designer. Eventually it may evolve into a softsynth management application that allows the user to control and manage a variety of command line softsynths, but it currently just wraps the excellent Fluidsynth program.