What are some alternatives?
When comparing Quill by Story Studio and Tilt Brush by Google, you can also consider the following products
A-Painter - Paint in VR in your Browser
Snap Art - Snap's augmented reality platform
Oculus Medium - Sculpt, model and paint in virtual reality on a 3D canvas.
SprayPrinter - Convert digital designs into wall art from your smartphone
MasterpieceVR - Powerful VR sculpting & painting tool
Kingspray Graffiti - Collaborative graffiti simulator with realistic spray and drip effects.