This software creates 3D models by intersecting a top, front, and side view. By combining this with layers, you can create complex geometry easily simply by drawing from different directions.
The name Itmas comes from the fact that it's "impossible to model a sphere". Intersecting three circles gives you a 'Steinmetz solid' and not a sphere.
The 'export' button allows you to export a .vox model, which is used in voxel software such as MagicaVoxel.