Piper
1.0 Beta by Mike Weber uses BSplines to make Pipes in POV-Ray plus make spline based animation paths

SpilinEditor
SpilinEditor is a graphical curve editor by Alessandro Falappa mainly designed for POV-Ray 3.0x raytracer. You can draw and edit 2D cubic_spline curves used in LATHE and PRISM primitives then obtain a 3D shaded preview (via OpenGL library) of the corresponding object. It takes advantage of an accelerated video card if present.

Steve Abbott's Celtic Knotwork for POV-Ray
Steve Abbott's Computer Drawn Celtic Knotwork. A program is available for download to draw Celtic knotwork that can output in POV-Ray format.