Cairo - Cairo is an open-source 2D graphics library released under the GNU Lesser General Public License with support for several output devices.
Pixi.js - Fast lightweight 2D library that works across all devices
Anti-Grain Geometry (AGG) - Anti-Grain Geometry (AGG) is an open-source 2D graphics library that provides you with tools to create multiple shapes and also comes with detailed documentation for explaining all the important concepts.
D3.js - D3.js is a JavaScript library for manipulating documents based on data. D3 helps you bring data to life using HTML, SVG, and CSS.
PlotDevice - PlotDevice is a graphics language for tinkerers, designers, developers and is written in Python.
Raphael - Raphael.js is an Object Oriented drawing library. It is good at making in-depth diagrams with complex interactions.