Mandelbulber - A 3D fractal renderer.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
3D-Coat - 3D-Coat is the one application that has all the tools you need to take your 3D idea from a block of digital clay all the way to a production ready, fully textured organic or hard surface model.
TouchDesigner - TouchDesigner is a visual development platform that equips you with the tools you need to create stunning realtime projects and rich user experiences.
TrueSculpt - Model a virtual clay ball by pushing or pulling it with your fingers.
Structure Synth - Structure Synth is a tool for creating 3D structures from a set of user specified rules.