It would be cool if it included sample OBJ files to entice me to find my own later. Otherwise I feel like I just hit a wall immediately in the app will probably not try it again.
Specifically I tried this rook from this chess set. https://www.thingiverse.com/thing:5994219/files
Sadly, some of the crenelations on top of it are just cubes with 2 sides missing that would be impossible to attach to the folded up rook. I imagine there is a ton of loss between a file for a 3D printer, a random convert to Obj with no settings, and this net maker, so I'm not unsympathetic to the problem. It's just that this is a printout that would not be foldable into something useful.
This one is called Unfolder, it's a different app, made by a different person, etc...
More than one app per category can exist, and that's good!
A 3D model unfolding tool for creating papercraft
Also avaliable on Mac App Store
Unfolder can generate 2D parts for your 3D models in a few seconds. The unfolding algorithm is smart and highly optimized for papercraft to minimize your effort in further editing.
Even though the auto-unfolded result is decent most of the time, Unfolder also allows you to split and join parts easily by clicking the edges in 2D view or 3D view.
Unfolder allows you to switch, add, remove, merge, and reshape the flaps. Furthermore, it can optimize the shape of flaps automatically to avoid the collision.
Unfolder allows you to customize the color, width, and dashing of lines. You can individually control the appearance of the cutting line, ridge-fold line, and valley-fold line.
Whether you want to print the template, edit it in external applications, or cut it using a CNC machine. Unfolder let you export in various formats for different purpose.
Also avaliable on Mac App Store