My favorites are Chaoscope, XD, Apophysis and nowadays UF. Whish i could write my own formulas for it but i just can't get into it sigh. So I start from a given formula and zoom into and tweak the coloring parameters until some totally different creation comes out. What i like very much here is the ability of layering. With Chaoscope i can create images without the overloads of functions of other programs, just simple. I love the wonderful strong colors that come out sometimes and the endless variety of interesting attractor designs. And most of all...it's free! XD fascinates me because of the 3D ability. Whish there will be mesh export to Cinema 4D or other rendering programs with the next update. Well and about Apo i don't think i have to explain much ;-) To me the best flame creator!