I first encountered the concept of "clean room" in the context of Sean Lahman's free baseball stats database. While technically baseball stats are free, their compiling and manner of presentation in any given format may be claimed as proprietary by any particular provider. And so there's an extensive volunteer effort from baseball fans to "clean room" source them from independent sources such that they are verifying the stats independently of their provenance as a legally permitted basis for building out the database.

I even recall Baseball Mogul relied on the Lahman DB for a period of time. It does make me wonder if we'll see more of that.