Have you heard about forger? It is a digital sculpting app for iOS that is basically ZBrush available anywhere. You can sculpt while you are on the train, waiting in a queue — literally anywhere.

The toolkit features an intuitive multitouch interface, a number of brushes, the ability to import/export OBJ files, and lots of other amazing features. It is capable of concept sculpting, multi-resolution sculpting, subdivision rebuilding, masking, partial visibility, topological symmetry scanning, sculpt layers, remeshing, auto-retopo, and more.

You can even paint several texture channels (baseColor/metalness/roughness) per mesh, and multiple layers per texture channel, with masking support and adjustment layers using a regular paintbrush or a projection paintbrush.