Hi @PhilippBuxbaum ,
There are actually quite a few ways to do this in ZBrush.
- Mesh from Mask. Quickly sketch out 3D meshes using a variety of specialized masking brushes. Remember that alphas can be applied to masking strokes.
https://help.maxon.net/zbr/en-us/Content/html/user-guide/3d-modeling/sculpting/sculpting-brushes/mesh-from-mask/mesh-from-mask.html
- Mesh Extract–another way to quickly create a new mesh on a surface using applied masking:
https://help.maxon.net/zbr/en-us/#html/user-guide/3d-modeling/modeling-basics/creating-meshes/mesh-extract/mesh-extract.html?Highlight=mesh%20extract
- Topology Brush–draw out new low poly geometry over a surface using curves and extrude a mesh from it:
https://help.maxon.net/zbr/en-us/Content/html/user-guide/3d-modeling/topology/topology-brush/topology-brush.html
- The Snapshot 3D feature of Spotlight can be used to create a mesh from a 2D alpha image through another mesh:
https://help.maxon.net/zbr/en-us/#html/user-guide/3d-modeling/modeling-basics/creating-meshes/snapshot3d/snapshot3d.html?Highlight=snapshot%203d%20spotlight
- Any simple B&W image can be turned into a 3d mesh with Alpha> Make3D.
- Many brushes with the “Curve” prefix like “CurveQuadFill” can be used to quickly draw out meshes using a combination of curve strokes.
When you take into account that polygroups, polypaint, and masking can all be converted into the other, there are a dizzying number of possibilities to create meshes from polygroups, masking, color, or even an applied texture using UVs.
Hope that helps! 
