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GCut

The GCut addon provides a set of tools to model and create mesh with greasepencil strokes. It has also a set of tools for making booleans and another set of tools useful when sculpting.

The CGut addon offer the following features

GCurve:

GPTube. To convert a grease pencil òr annotation stroke into a curve. Best is to use the grease pencil stroke so you have more control. For examle you can stabilize strokes with the grease pencil. After pressing the GPTube button you will see a quite dense mesh. Probably an idea is to enable POLY in the panel on the left bottom. When finished you still can simplify the Curve in the N-Panel > GCurve > Simplify Curve. You can also change in the N-Panel the thickness of bevel and resolution.
GPScrew. First you make a grease pencil stroke in orthographic front view and then you go out of draw-mode. (Go in Object-mode). Then you press the GPScrew button and you will see the effect applied. At the moment, when you change anything in the panel on the left bottom, Blender seems to crash. But luckily most functions are available in the N-Panel > GCurve. You will want to simplify the curve because it looks quite dense.
GPStretch. Select the object, then the stroke. Best is to use a mesh that has enough poly count. The mesh will then deform to the grease pencil stroke.

GCut:

Free Hole. You will see three modes: Hard, Soft and Cut. Generally with Hard you will have a kind or hard-surface mesh. The soft-mode gives you the same but then remeshed, and looks smoother. And Cut is what you want to do to Cut, or perform boolean with the greasepencil. When you want to cut, first make a stroke. Then select the object then the stroke and then you press Free Hole.
GPCutter. Same as above. Quite hard to explain but it seems to combine the grease-pencil stroke and the contour of the mesh. Best is to watch the video or try it out. One thing to keep in mind is always select the object first and then the stroke before performing an operation.
GPLiner. Cuts a line, a bit thicker than the stroke is. Select objet first then stroke before performing an action. Check also the different modes: Hard, Soft and Cut.
GPShaper. To make shape with grease-pencil stroke. Before performing action go out of draw-mode.

There are some other feature for example to perform boolean operations, remesh, flood fill. The video below shows the features described in this post.