You can now download the latest stable (standalone) version of NCSpiral below. Currently (March 2014) the most up-to-date version is NCSpiral 6. More details are available in its readme file.
NCSpiral is a simple Java applet that generates and renders a mathematically correct and graphically precise Ulam's Spiral. It is customizable in terms of spiral size and color, and is currently in active development.
Many bug fixes are in the works, as always, and most of the bugs in NCSpiral are well known. I did make it for fun, after all!
Yes, I am aware that the color selectors currently do not, in fact, display the color you have selected...I am also aware that the applet is slow and opens the spiral in a new (pop-up) window.
It will also give you a security warning. Ignore it. Look through the source code (link below) if you still do not believe that my intentions are purely good. Perhaps not entirely practical, but certainly not ill-intended. :)