It will take some effort for you to learn how to use the Highstock library. The website is: http://www.highcharts.com. The demo's page shows all the types of charts Highstock supports: http://www.highcharts.com/stock/demo/spline.
To make my chart display splines, change line 310, which is a commented out line, to:
type: 'spline',
I noticed that spline slows the display down considerably with a large data set.