Jade is a cross-platform diagram editor built on the Qt framework.
Free drawing software for Windows, Mac OS X, and Linux
Interactive designer for Celtic knots
Not your usual Architectural Modeler
Output Processing script from Java AWT/Swing paint call
Business graphics diagramming application + customizable shape lib.
Create and edit SVG graphics directly in ownCloud. Based on svg-edit.
Inkscape extension to add and edit GNUplot graphs
A powerful C++ class library for image manipulation