Gfract is a GTK-based fractal program that implements the standard Mandelbrot and Julia sets. It features infinite image size with infinite anti-aliasing if you have the memory for it, Julia instant preview mode, user-specified coloring algorithms, and PNG support. For palette files it uses the same format as Fractint does, except that it supports arbitraly large palettes.
gif2png is a simple command-line utility to convert images from GIF to PNG format. It automatically preserves transparency, interlacing and text comments, and it can do multiple images in one command (e.g., gif2png *.gif). The distribution also includes a web2png script that can be used to convert an entire web tree; it calls gif2png to do image conversions, then patches IMG SRC tags correctly in referring pages.
Gifsicle is a powerful command-line program for manipulating GIF image files. It has good support for transparency and colormap manipulation, simple image transformations (cropping, flipping), and creating, deconstructing, and editing GIF animations. It can also optimize GIF animations for space. Also included is a GIF animation viewer and a program that checks whether two GIFs look the same.