A toolkit of sorts that I made for myself when I was working with low poly models. It is intended to be used to align parts of a model mathematically perfectly, I'm personally very pedantic about getting everything just right. I don't see how this could be used in high poly modeling but I find it essential in low poly modeling.
The blend contains 10 two dimensional faceless polygons with edges connecting the tips and middles. There is a single vertex at each point where two or more edges cross. In the image edges are black and vertices are highlighted in red.