There are 2 repositories under engraver topic.
Low Cost DIY Laser XY Scanner, Cutter, or Engraver
Simple engraving tool, compose scene with images and labels, create gcode and send it to your engraver.
The serial protocol analysis from the K3 laser
PyCNC-Web: A web interface for the Nikolay PyCNC and changes in the code to add a new axis supporting a Laser Diode so that the machine works as a cutter/engraver.
CNC – Mini Laser Engraver
Tool to calculate the duration of your cutting / engraving process
100% open-source laser cutter and engraver.
Only a "backup" for the Laser Engraver model K3 (manual, software & others).