I've been building ruby-libgd, a native Ruby binding to the GD graphics library.

This folder contains a Docker setup that runs JupyterLab with a full Ruby kernel — you can plot sin, cos, log, implicit curves like circles and ellipses, all in Ruby with no Python involved in the plotting.

The Plot class API ended up quite clean — plot.add("sin(x)") just works. Happy to answer questions about the implementation, especially the SafeMath evaluator and the implicit curve rendering.