Tracer
Tracer version 1
Tracer allows you to draw curves in TVPaint Animation.
You have settings for strenght, thickness and style.

Chose your curve type, add controls points in TVPaint Animation. Double click to set the last point. Then Tracer will draw a nice smoothed curve.
User's manual
TracerDemo
The Demo version is limited to 4 points. Ask for it : manuel@trionix.fr