Sculpting a complete Planar Head - Stylized Character Workflow - Blender Studio
Boolean Modifier — Blender Manual
How to Sculpt in Blender - Howchoo
GitHub - jayanam/fast-carve: Hardsurface utility Blender addon for fast boolean and bevel operations (it's now JMesh tools : https://github.com/jayanam/jmesh-tools)