s3d is an XML schema for 3d scenes, objects, and so forth (intended primarily but not exclusively for computer games). The problem is that often as a games developer you need to work with many 3d editing tools and rendering engines, and there should be an easy and portable way to move objects, levels, etc. around. By having a common intermediate file format, you only need to write one exporter per tool and one importer per graphics engine. Also, you can develop generic tools which are not tied to any particular engine.
Image Alchemy has the ability to convert between over 90 different raster image formats (including all colorspace and compression variations of each format). Color management features include gamma correction, undercolour removal, seven high quality dithers, colorspace conversion, and palette manipulation. It also includes a Postscript interpreter.
netpbm-free is Debian's fork of netpbm that was designed with security of code, reliability of interfaces, and freedom of software in mind. It is a suite of over 200 different programs from different authors, and is itself a fork of pbmplus. The suite supports almost every graphic format (including JPEG, PNG, BMP, ICO), and can create, change, crop, rotate, and transform in and between these formats.