Oxidizer is a very nice editor for fractal flames. Fractal flames take many shapes, here's some crude examples made almost literally at random by Oxidizer. Only the color scheme and the positioning have been altered.
Nicer examples can found on the home page for the Electric Sheep screen saver with which Oxidizer shares a common code base.
Both programs use the flam3 libraries to render the flames. This also means Oxidizer can read and write the flam3 file format used by Electric Sheep.