A slightly older one that produces very nice looking results for certain aesthetics is https://mewo2.com/notes/terrain/ https://mewo2.com/notes/terrain/ As wel

A slightly older one that produces very nice looking results for certain aesthetics is https://mewo2.com/notes/terrain/ https://mewo2.com/notes/terrain/ As well as also being open source, the page gives interactive demonstrations of each step that the process takes which is interesting. (edit: clicking round a bit more, Azgaar's project lists the one at mewo2 as on if its inspirations/influences)