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).
OpenIcons is a set of SVG icons intended to be used on the Web. All the icons are vector-based and made using InkScape. The icons can easily be converted from SVG to pretty much any common graphics format. Since the icons are meant to be used primarily on the Web, the default distribution of the icons includes PNG copies of all icons scaled to the following sizes: 16x16, 32x32, 64x64, and 128x128 pixels.
Toolbar Icons is a collection of free toolbar icons. All icons are available as (Inkscape) SVG files. OMake build scripts that automatically generate PNG files of basically any size (using Inkscape) are included. PNG files in a few default sizes (16 x 16, 24 x 24, 32 x 32, and 256 x 256) are prepared in .tar.gz archives.
Multicrush is a wrapper around pngcrush that distributes the work of brute-force compressing a single image over several pngcrush processes. This gets you a slightly less than a linear speedup, caused by different compression methods having slightly different durations. For example, the author has measured a speedup of 1.92 on a 2-core Intel T5300, and 3.86 on a 4-core Intel Q6600. The only requirements are a copy of pngcrush and at least Python 2.4. If you have version 2.6 or higher, multicrush can automatically detect how many CPUs to use.
Spectra is a simple tool designed to aid in evaluating the quality of random numbers generated by TRNGs and PRNGs. It does this by counting the occurrences of characters within a given input file to help detect perceived bias, and then visualizes the data as colored (or black and white) pixels in an image file to aid in detection of repeating patterns. As the human mind is exceptionally good at picking up on patterns that might otherwise be difficult to detect mathematically, Spectra allows the user to rapidly make a determination on the repeatability of numbers generated from the suspect RNG.