The converter, the two sums you do around it, and a pattern maker for drawing a chart by hand. Everything runs in the page you are reading: nothing is uploaded, and there is no account to make.
Neither of them asks for an account and neither sends anything anywhere: they are arithmetic and a colour table running in the page you are reading. They exist because these are the sums a stitcher does on the back of an envelope before starting, and getting one of them wrong costs a piece of cloth or an evening.
A blank grid, or the chart you have just converted, and the tools of a drawing program — pencil, bucket, line, mirror — with DMC stranded cottons as the only colours. It downloads and publishes like any other chart.
Stitches in, centimetres out: the finished motif, the piece of cloth to cut with its margins, how many strands to use, and how far one skein goes. Aida, evenweave and linen, over one thread or two.
Paste a hex value or an RGB triplet, or pick a colour, and get the DMC stranded cottons nearest to it, sorted by how different they look to an eye rather than by how close the numbers are.
The two calculators are the quick end of the site. The long end is a chart of every plain-cotton DMC shade with a page for each one, a converter that turns a photograph into a chart made of those threads, and a guide written for somebody who has never followed a grid before.