NOTE: This video by Zach Reinhardt is very informative as well, I highly recommend watching: https://youtu.be/2hEHtKH55Us
In this quick video I go over a few built-in retopology tools that will make your life easier without having to resort to any addons.
There are very few good retopology addons for blender, and those that are somewhat acceptable usually cost $$, even though they hardly improve on the existing toolset.
This tutorial is aimed at beginner and intermediate level blenderheads. If you practice these techniques regularly, you can become pretty fast and efficient at manual retopology in blender. Good luck 🙂