3D fractal software that lets you use a custom ruleset?

[opusGlass]

Hi guys,

I've had an idea for an alternative to the Mandelbulb as a 3d version of the Mandelbrot and I want to get some good images of it before I start telling people about it. Problem is, I write my own fractal generating programs and the 3D generators I've built don't produce very high quality images. Is there a (free) 3D fractal generator out there that allows you to define your own rule sets? I just need to use the escape radius like normal but my ruleset isn't one that's going to be found in any presets.