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.

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

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.