What are some alternatives?
When comparing A-Painter and Oculus Medium, you can also consider the following products
Tilt Brush by Google - Paint in spaces around you with Virtual Reality
MasterpieceVR - Powerful VR sculpting & painting tool
SprayPrinter - Convert digital designs into wall art from your smartphone
VR Sketch - A tool for designers to draw inside virtual reality
AI Painter - Turn your photos into paintings
Quill by Story Studio - Paint in virtual reality on an infinitely scalable canvas