Pretty much what it says on the tin. Europeans had forgotten or lost the atlatl and lithic tool making crafts by the modern period (well before in most cases). The challenge is to keep those technologies alive in Europe to a degree where people at least know that lithic artifacts are man made tools and atlatls are known in at least principle, at a minimum. Extra points if every village has a knapper as well as a miller and smith, and/or atlatls are used as commonly as other peasant weapons.