Goxel is a 3D program that lets you create voxel volumes, a bit similar to minecraft. The code is Open Source and fully available on Github.

Features:

• Unlimited scene size: You can create voxel images as big as you want.
• Layers support: Decompose your image into several layers for easy editing.
• Many export formats: Goxel can export to obj, pyl, magica voxel, png, qubicle, povray, and more.