Something like https://www.camptocamp.org/ might be what you are looking for.
hiking
For Backpackers,Trekkers and Hiking Tips, trip reports and gears
That is along the lines of what I'm looking for, but, unfortunately, I'm not a fan of their license (CC BY-NC-ND 3.0) — it's a bit too restrictive for something that I would personally want to contribute to.
I wish there was something like that built using openstreet map. The maps are already pretty good but it would be useful to get comments.
Agreed!
Osm actually does have hiking trails marked (with difficutly levels too) and you can use apps like OsmAnd or Organic Maps to view them with comments - I've been using it for backcountry hikes where I need offline maps and it's pretty reliable.
Yeah, I use it too.
By "comments" I mean, like with alltrails, since a lot of people are using it, you often see up-to-date comments about the current trail's condition. Like when it's muddy in the spring.