In the text window for extrusions there are two options: one-sided and two-sided. I propose adding a 3rd option "skewed". This would create a one-sided extrusion but the path of the extrusion would not have to be perpendicular to the sketch plane. I'm not sure how useful this would be so maybe we should discuss it.

My 2 cents, this adds some ability to create different geometry but may not actually be that useful. I'd hate to see it abused to make things that are already hard to make in SolveSpace.

Implementation:
Low complexity - this is a good item for someone new to the SolveSpace code.
Tasks:

1. Add a 3rd subtype to the group class.
2. Add the appropriate checkbox in the text window.
3. Make sure it is treated as one-sided in all the right places.
4. Don't apply the perpendicular constraints to the extrusion vector for this subtype. (extrude is already implemented as 3 DoF with 2 internal constraints you don't see).

The image here shows independent constraints that would normally be fixed to 90 degrees. This can be hacked in code by commenting out 2 lines that apply those 2 constraints.