What are some alternatives?
When comparing PaintCube and Kodon, you can also consider the following products
Substance Painter - Substance Painter is a 3D painting software allowing you to texture, render and share your work.
A-Painter - Paint in VR in your Browser
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Oculus Medium - Sculpt, model and paint in virtual reality on a 3D canvas.
Mari - Mari is 3D painting without limits, combining the power and performance to handle even the most complex assets with artist-friendly 3D paint tools.
MasterpieceVR - Powerful VR sculpting & painting tool