The Donut chart was formerly a separate chart, however it's now simply a variant of the Pie chart.
<script>
window.onload = function ()
{
var data = [45,57,48,32];
var donut = new RGraph.Pie('myDonut', data);
donut.Set('chart.labels', ['Jan', 'Ben', 'Mark', 'Lucy']);
donut.Set('chart.linewidth', 5);
donut.Set('chart.strokestyle', 'white');
donut.Set('chart.tooltips', ['Jan', 'Ben', 'Mark', 'Lucy']);
donut.Set('chart.variant', 'donut');
donut.Draw();
}
</script>