Prima is an extensible Perl toolkit for multi-platform GUI development. Supported platforms include Linux, Windows NT/9x/2K, OS/2, and UNIX/X11 workstations (FreeBSD, IRIX, SunOS, Solaris, and others). The toolkit contains a rich set of standard widgets and has emphasis on 2D image processing tasks. A Perl program using Prima looks and behaves identically on X, Win32, and OS/2 PM.
pngquant is a batch conversion utility to quantize and dither truecolor PNG images, especially those with a full alpha channel, down to "RGBA-palette" PNGs (i.e., PLTE + tRNS in PNG parlance). Such images are usually two to four times smaller than the full 32-bit versions, and partial transparency is preserved quite nicely. This makes pngquant especially useful both for Web sites and for PlayStation 2 development, where one of the texture formats is RGBA-palette-based (though not PNG-compressed).
The pnmtopng package contains the official pnmtopng and pngtopnm utilities for use with the rest of the PBMplus/NetPBM suite. They are among the best PNG-supporting applications available, with automatic detection of grayscale or palette images and excellent heuristics for creating the smallest possible PNG images.
These are the demo programs that accompany O'Reilly's "PNG: The Definitive Guide." rpng is a simple file viewer with the ability to set a background color when displaying transparent PNGs. rpng2 is a progressive PNG viewer, designed to work like a web browser (though it contains no network code); it can generate a background image when displaying transparent PNGs. wpng is a simple converter from NetPBM to PNG format; in most respects it is much more limited than pnmtopng, but it supports interactive entry of PNG text annotations and will generate noninterlaced PNGs on the fly (rather than buffering the entire image first like pnmtopng). The viewers include simple front ends for both X and Win32; the converter is a command-line app that compiles on Unix, Windows, and probably other platforms.