Instant meshes free quad reduction tool

Instant Meshes:

Free retopology software:

https://github.com/wjakob/instant-meshes

Video here: https://www.youtube.com/watch?v=9sV88Z3cXdY

Check the Blender equivalent BSurfaces: https://wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.64/Bsurfaces_1.5