Maybe something like this could work as a categorization:
Manual editing:
- Paint
 - Draw
 - Erase
 - Level Tracing
 - Scissors
 
Semi-automatic editing:
- Threshold
 - Grow from seeds
 - Fill between slices
 - Watershed
 - Fast Marching
 - Flood Filling
 
Global editing:
- Margin
 - Smoothing
 - Logical operators
 
Modeling:
- Draw Tube
 - Surface Cut
 
Volumes:
- Mask Volume
 - Split Volume
 
How would you use these categories?
That’s interesting and indeed it would be quite easy to implement (by adjusting the style sheet). Let’s see what other users/developers think.