Blender Softwrap

armagon

Very interesting way of doing retopos: https://blendermarket.com/products/softwrap

thomasp

Looks cool for sure although the platform requirements would worry me a bit (e.g. no Mac version at all?).

But for retopo or generally working on top of a 'live' surface the shrinkwrap modifier in combination with vertex groups and standard modelling tools is a very workable solution IMO.