This is the donut chart. It's essentially a pie chart with a big hole in the middle. You can use the pie chart properties when customising the donut.
The example file is here.
<script> window.onload = function () { var data = [45,57,48,32]; var donut = new RGraph.Donut('myDonut', data); donut.Set('chart.labels', ['Jan', 'Ben', 'Mark', 'Lucy']); donut.Set('chart.linewidth', 5); donut.Set('chart.strokestyle', 'rgba(255,255,255,1)'); donut.Set('chart.tooltips', ['Jan', 'Ben', 'Mark', 'Lucy']); donut.Draw(); } </script>
Please see the Pie chart documentation for what properties you can set. Most of the pie chart properties are available on the donut chart too.