alt Hacker NewsThe license seems to already require this: https://www.openstreetmap.org/copyright/
Maybe I am misunderstanding the summary, but it says: "If you publicly use any adapted version of this database, or works produced from an adapted database, you must also offer that adapted database under the ODbL." <https://opendatacommons.org/licenses/odbl/summary/>
Yeah the problem is what's considered an adapted database. If it was strict it would mean apps like Alltrails (which is 90% openstreetmaps data) would need to list their trailmaps as open databases, but they don't.