List 3D Software (Freeware/Open Source)

[Arg Arg]

create a voxel model with brushes or extrude pixel-art images.
Boolean-Operations.
paint on the model.
supported OBJ export.
easy to use.
check out the "MagicaVoxel" features and tutorials on youtube.

a great Open-Source-App called:

MagicaVoxel

- a free lightweight 8-bit voxel editor and interactive path tracing renderer
- Export Mesh with Baked AO and Soft Shadow
- Support Voxel Shader, Enhanced Brushes, Marching Cube Export
- Support Transparent voxels with Refraction and Attenuation
- support 2048^3 Volume, 16-bit Color/Normal

https://voxel.codeplex.com/