Project Vox is described as 'A free voxel editor from Big Bad Wofl'. There are more than 10 alternatives to Project Vox for a variety of platforms, including Windows, Mac, Linux, Online / Web-based and Steam. The best alternative is 3D-Coat. It's not free, so if you're looking for a free alternative, you could try MagicaVoxel or Goxel. Other great apps like Project Vox are VoxelShop (Free, Open Source), Voxel Builder (Free, Open Source), Acropora (Paid) and Cubik Studio (Paid).
Voxel Builder lets you easily create and edit 3D voxel graphics right in your browser. Simply select a colored block and click to draw. Zoom in and out with the mouse and click and drag to navigate around the 3D canvas.
Model in a unique cubic style. Start modelization with boxes. Move, rotate and scale cuboids. Apply one or more textures per cube, disable any face, edit UV coordinates and create any character parts without the constraints of voxels.