Unfold tool or similar?

Assume I have an object with a curves or compound angle. What tool can I use to unfold or flatten it to create an accurate template for cutting out of sheet goods?

Can you post the file?

Squish or Smash.

The surface has compound curvature so it will not flatten without shrinking and/or stretching. Squish has several options for the surface deforms to flatten. The “accuracy” of the result will depend in part on how well those options match the behavior of the physical material, and also on how the object is fabricated.

depending on how the object is to be fabricated an alternative may be to divide the surface into small surfaces which are close enough to developable to unroll without significant deformation. The object would then be made by assembling those smaller surfaces.