EDM is a subtractive machining technique, similar in principle to milling, laser cutting, waterjet cutting, etc. This particular material removal method is an electric arc. It's typically used for cutting very hard materials like titanium, 2D shapes with very very thin kerf, or thin, deep holes.
This repo documents a CNC sinker EDM. Nominally for etching PCBs, but that's unproven.
Early days. Several components of the tech have been tested and proven. Code rewrites are planned. Bits and pieces of schematics for different components are done, but more are needed, and they must be combined into one.
I would not recommend paying much attention to this repo just yet.
See http://www.jrainimo.com for occasional project updates.