Blender - Blender is the open source, cross platform suite of tools for 3D creation.
MagicaVoxel - A free lightweight GPU-based voxel art editor and interactive path tracing renderer.
SketchUp - 3D for Everyone
Goxel - Goxel is a simple, but powerful voxel graphic editor with 24-bit color support, unlimited scene...
AC3D - AC3D is a 3D software for games, virtual reality and flight simulation, scientific, medical and general data visualisation, rapid prototypes of 3D designs, 3D printing, Google Earth, X-Plane, Second Life and more.
Cubik Studio - Model in a unique cubic style. Start modelization with boxes. Move, rotate and scale cuboids.