CNC & Machine Tools (Industrial & Building Automation): open-source projects that exist because someone reverse engineered a closed product, sorted by GitHub stars.
Inkscape extension driving Silhouette vinyl cutters via their reverse-engineered USB protocol
Laser software for K40 (reverse-engineered M2 Nano/Lihuiyu), GRBL and fibre lasers
Pure-Python implementation of Heidenhain's LSV2 CNC control protocol
Open-source firmware for the CNC3018 offline controller
Reverse-engineered protocol and file format of Ruida laser controllers (RDWorks, USB, Ethernet)
Decoder and tooling for the scrambled RDWorks .rd laser file format
Inkscape extension to drive Ruida-based laser cutters directly
Notes on hacking the machine code of RuiDa laser controllers
Interpreter and renderer for Ruida .rd laser job files
Reverse engineering of the LaserWorks/RDCAM software from Shenzhen Reader Technology