Interesting project. Surprised no one has done this before.
I was fairly surprised too. I actually started this project some years ago because I got tired of waiting for someone else to do it!
For a long time I was using it (even in a couple of commercial projects) in a pretty terrible state. I finally got some time over Christmas to polish it up a little.
how does the lightmap baking work? Does the program do the unwrapping, and apply it to UV2? how would I use it in Godot, for example, or Urho 3D?
Pretty much, it unwraps all the faces, for each fragment it does a ray intersection between each light in the scene and works out the distance, the lights strength and if anything is blocking it.
It is currently set via code to do zero reflections and is multi-threaded so is pretty fast (could even be real time I suppose).
The preview program that it runs to let you test the map then reads this second lightmap in and uses it for shadows. (I have both an OpenGL version and a 100% pure software rendered version I made for a games jam.). If you are familiar with the .obj wavefront format, the lightmap coordinates are stored as an extension as 'vl' entries.
Actually I have a nifty video of the software renderer using the generated output here:
I am sure a very few will get use from this but thanks
Cannot agree more with the statement about general 3d tools lacking that which some Quake editors have.