Ultra Fractal - A fractal rendering program. There are many tutorials available on the site and on DA. Updated 2017.
Polyfractalisation - Inside the Mind of an Apophysisist. Great Tips and tutorials by IDeviant (https://www.deviantart.com/ideviant)
Agony - A fractal Program by kelbv (https://www.deviantart.com/kelbv) Updated 27 February 2011
Flam4 - A fractal flame renderer. Version 0.87 as of 18 August 2010
Incendia - by Aexion (https://www.deviantart.com/aexion), A 3D Multiprocessor Fractal Engine
There is also a Chat room for information here http://chat.deviantart.com/chat/Incendia
There is also an Incendia Material Tutorial page here http://aexion.deviantart.com/art/Incendia-Material-Tutorial-1-99987251
Recent version is I