HDA to create a square spiral....but you don't have to be square, change it to hexagonal (60) if you like. (no Vex required.)
DL link in the tube video.
(could probably tweak for angle of 120 for a triangle too...but can't be arsed).
Note: if you try to bevel the corners, if divisions is ODD, the midpoint will go missing, if it is EVEN, it works. The bug appears only for multi curves that have been joined/fused together, ie. on a default grid, it works fine. I have reported this bug to SESI.