Structure Synth Alternatives

Blender is the open source, cross platform suite of tools for 3D creation.

Mandelbulb 3D is a free software application created for 3D fractal imaging.

A 3D fractal renderer.

Fractals and visual effects generator

TouchDesigner is a visual development platform that equips you with the tools you need to create stunning realtime projects and rich user experiences.

C++ and Java programming at the speed of thought.

Fragmentarium is an open source, cross-platform IDE for exploring pixel based graphics on the GPU.

Dead Deer is a 3D modeler, 3D game maker, and a 3D demo maker designed to create games.

openFrameworks

Bforartists is a fork of Blender.

Unreal Engine 4 is a suite of integrated tools for game developers to design and build games, simulations, and visualizations.

The multiplatform game creation tools for everyone.

blendersensei.com/sensei-format Makes using Blender easier by overhauling its interface & tools.