Draw screenshot DRAW – from a quick sketch to a complex plan, DRAW gives you the tools to communicate with graphics and diagrams. With a maximum page size of 300cm by 300cm, DRAW is powerful tool for technical or general posters, etc.
GraphicsMagick is the swiss army knife of image processing. Comprised of 259K physical lines (according to David A. Wheeler s SLOCCount) of source code in the base package (or 900K including 3rd party libraries) 
ImageMagick is a software suite to create, edit, and compose bitmap images. It can read, convert and write images in a variety of formats (over 100) including DPX, EXR, GIF, JPEG, JPEG-2000, PDF, PhotoCD, PNG, Postscript, SVG, and TIFF. 
FontForge is an outline font editor that lets you create your own postscript, truetype, opentype, cid-keyed, multi-master, cff, svg and bitmap (bdf, FON, NFNT) fonts, or edit existing ones
mtPaint is a painting program which Mark Tyler developed from scratch so he could easily create pixel art and manipulate digital photos