This is two mesh vertices relaxation algorithm with none to low shape shrinkage, usefull for mesh editing
I don't know much about "vertices relaxation algorithm", but after quickly glancing over the patch this appears to be a particle polygoniser (?!). Apparently it is using the same marching cubes approach as the fluid system and mantaflow, at least the hash tables are the same, and they're pretty unique.
If it's worth the effort, and if OP agrees/isn't responding, I can give this patch a nice try and update.
farsthary was searching a way to make a particle polygoniser for sph paricles he implemented in Blender.
But he began to familiarize himself with these algorithms by making modeling tools like this one or sculpting tools like voxel sculpting experiments and unlimited clay.
These tools are mesh editing tools. They had same options to lock borders. They inspired to psy-fi Relax brush for UVsculpt.
It seems that no update was done since 2.5x series. Patch probably can not be applied as is. It is so old.
I am not sure these tools have an interest since we have Laplacian smooth modifier.
Maybe it is still interesting to add HCrelaxation algorithm as a mesh editing tool, modifier or sculpt brush.
I don't know what campbell, apinzof or psy-fi think about it.
I had some time to kill, dug around, and the patch attached here is the wrong one (mistakes happen :) ). This is a particle polygoniser (maybe for the SPH particles), not a mesh relaxer. It does apply nicely to master (only 3 .rej of a couple lines that can easily be re-implemented) but it is incomplete and it's adding a couple of files that are not compiled.
You are right. Description does not correspond to attached patch.
If there is an hope to obtain a polygoniser that works from this patch, it would be great to see a resurrection of this.