3D->2D & 2D->3D

• PEPAKURA Designer

http://www.tamasoft.co.jp/pepakura-en/

• Paper Model plugin pour blender

https://wiki.blender.org/index.php/Extensions:2.6/Py/Scripts/Import-Export/Paper_Model

• 123DMake

http://www.123dapp.com/make  Turn your amazing 3D models into even more amazing build-your-own projects.

• Sketchchair

www.sketchchair.cc  SketchChair is a free, open-source software tool that allows anyone to easily design and build their own digitally fabricated furniture.

• Sketchup plugin for folding paper

http://www.pumpkinpirate.info/flattery/

• Lithophane
  

 images (greyscale) to 3d print or CNC mill as low relief ("bas-relief") or lithophane http://3dp.rocks/lithophane/(free, online software)

• FlatFab
  

http://www.flatfab.com/

• HGT2STL, convert a picture (greyscale) to a 3d file. http://www.thingiverse.com/thing:110904