Cairo - Cairo is an open-source 2D graphics library released under the GNU Lesser General Public License with support for several output 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.
Skia - Skia is an easy-to-use and user-friendly 2D Graphics Library that comes with many prominent APIs for usage in software and hardware platforms.
Bgfx - Bgfx is an open-source, high-performance, and cross-platform graphics API agnostic style rendering library that gives you the tools to create high-profile video games without limitations.
Raphael - Raphael.js is an Object Oriented drawing library. It is good at making in-depth diagrams with complex interactions.
SkiaSharp - SkiaSharp is a simple yet robust, cross-platform 2D graphics API designed from scratch for .NET platforms based on Google’s Skia Graphics Library.