I know there's a really cool name for these ridgeline plots but can't quite recall what it is at the moment.
Joyplot. I even have a Twitter Moment about these plots.
However, the term joyplot has fallen out of favor with some bioinformaticians since it derives from an album cover which derives from a band name which derives from a novella that uses the term "Joy Division" for a concept that derives from the Holocaust.
Oh dear. I guess I'll stick with ridgeline then!