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).
DatePNG is a PHP class can be used to generate a PNG image with a given time. It opens a template image in PNG format and renders text with a time in one or more formats. The font, size, position, angle, and color of the text are configurable parameters. The resulting image is generated in the PNG format as the current script output.
WS Charts is a PHP class that can be used to render charts of several types. It takes a list of values that define points of one or more sets and renders charts of several possible types: line, bar, surface, and pie. The class provides options to choose colors, gradients, show coordinates, etc. The generated charts can be saved to a given file or displayed as the current script output.
SVGpage is an application that will render PNG images as SVG files or convert an SVG file to a PNG image. It uses an internal version of Autotrace. This is not a straight conversion to SVG (as there really is no such converter) but it does a fairly literal job with simple shapes, and renders a "painterly" effect for more photographic-style images.
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.