Mandelbulber - A 3D fractal renderer.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Cinema 4D - Cinema 4D is a 3D modeling, animation, motion graphics and rendering application.
TouchDesigner - TouchDesigner is a visual development platform that equips you with the tools you need to create stunning realtime projects and rich user experiences.
V-Ray - Learn why V-Ray for 3ds Max’s powerful CPU & GPU renderer is the industry standard for artists & designers in architecture, games, VFX, VR, and more.
Structure Synth - Structure Synth is a tool for creating 3D structures from a set of user specified rules.