Hi,
I wanted to share with you some usefull and free retopo tool : Instant Meshes.
It's instant retopology with some control as there is many options to dig.
After using it some time here is my short review :
+ Free and open source
+ Instant Retopology
+ Multi platform
+ independant program
+ portable
+ Symmetry detection option
+ Great results on organic models
+ Great to do a first retopo pass before manually deleting edge loops for example
- Need high resolution polygon count to get acceptable result for hard surface retopology
- Edge detection for hard surface not so great
- Would need Line tool using start and and point instead of drawing a line manually
