Songwrite is a tablature editor. It supports many string instruments in addition to traditional staff notation. You can edit tablature (guitar, bass, banjo, etc.) and staff notation, add lyrics, create your own songbook, play your partitions, print your partitions and your songs, automatically convert staff notation to tablature and vice-versa, export songs to many formats (PDF, MIDI, ASCII tablature, GNU Lilypond, LaTeX, PostScript, etc.), and import Guitar Pro 3/4 files (experimental).
PyMP3Cut is a Python command line tool designed to cut huge (> 100MB) MP3 files at high speed without requiring the extra disk space and processing time usually needed by visual audio editing tools, which convert the MP3 format to more easily manageable formats like WAV before doing anything. It reads and cuts simultaneously according to the autodetected MP3 frame rate and a timeline passed as a command line argument. It doesn't currently deal with Variable Bit Rate (VBR) MP3 files, though.
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.
EZFB is a polymorphic, object oriented Linux frame buffer API written in C, designed to adapt at run time to control any properly configured Linux frame buffer video system. It offers independent, simultaneous control of multiple video cards within a single system, exceptional control of colors, the ability to display all or portions of bitmap files anywhere on the screen, automatic color depth conversion, the ability to capture to bitmap files, an 8x8 bitmapped font, routines to draw points, lines, outlined and filled rectangles, signal trapping for automatic screen clean-up at process termination, and much more. The demonstration applications include a bitmap viewer, screen capture utility, screen saver, and a touch screen calibration utility and an application for generating, viewing, transforming, and saving files according to The International Laser Display Association's ILDA file format.
Allegro Sprite Editor (ASE) is a program specially designed with facilities to create animated sprites that can be used in some video game. It lets you create static images, characters with movement, textures, patterns, backgrounds, logos, color palettes, etc. It focuses on pixel editing to do pixel art. It isn't a photo retouching tool or a vector graphics editor. Mainly, it is a tool to create tiny animations pixel-by-pixel.
Evolvotron is an interactive "generative art" application to evolve images/textures/patterns through an iterative process of random mutation and user-selection driven evolution. If you like lava lamps, and never got tired of the Mandelbrot set, this could be the software for you. It's implemented using Qt, and is multithreaded.