Pepakura Designer is not available for Mac but there are a few alternatives that runs on macOS with similar functionality. The best Mac alternative is Unfolder. It's not free, so if you're looking for a free alternative, you could try FlatFab or Dunreeb Cutout. If that doesn't suit you, our users have ranked nine alternatives to Pepakura Designer and four of them are available for Mac so hopefully you can find a suitable replacement.
Unfolder is a 3D model unfolding tool to help you create papercraft easily and quickly.
Unfolder is the most popular Mac alternative to Pepakura Designer.
flatfab is software that helps you design and fabricate 3D objects. We imagine in 3D but ideate and draw in 2D. flatfab seamlessly does both.
It's not a papercraft specialized tool
Cutout is a plugin for Autodesk Maya for the purpose of building real paper models out of paper from your virtual 3D models.
UVMapper Professional is a stand-alone texture mapping utility for the creation and modification of UV coordinates for n-sided polygonal 3D models.
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From the alternatives listed this is the one most closely resembling Pepakura in design and feature set. In the version I'm trying now I'm ridiculously bothered by the way zooming works, but apart from that (from a first glance at least) it seems like it's the obvious mac counterpart to Pepakura.