Curvature – Find Twisty Roads (roadcurvature.com)

nifty. What this highlights in my locale is my favorite roads, the algorithm seems to work pretty well for the small sample I can attest to.

Tail of the Dragon is hard to beat: https://tailofthedragon.com/

I once played around with taking the curvature of mouse movement: UI-driven movements tend to be direct, low-curvature paths, leaving high-curvature paths free for binding (eg for scrolling).