SculptyPaint is a small free program to create 3D images. It was created with the intention of creating objects for the game Second Life, but is also able to export files that can be viewed in other programs. SculptyPaint is developed in JavaScript and includes diverse tools for creating 3D models. There are ten tools in all, each one in a different colour. Just click on any of them to see their options.
Any alteration done is automatically viewed, and in case of a mistake there is the useful Undo option. It has three rendering options (64x64, 32x32 and 16x16), that you can choose according to your needs. The resulting images are saved in PNG format.