On this topic: Tales of Maj'eyal is an open source game, but the game content is not. I was surprised to learn this, and it seems open source games isn't a complete non-starter like you might expect.
Richard Stallman has a policy of putting his non-engineering works under a non-libre license (CC-BY-ND 3.0) [0] [1], so maybe he wouldn't have a problem with this non-libre game as the underlying code is libre, just not the assets.
In my opinion, this is one of the problems with Stallman's "moral authority" approach to the FSF. I would very much like to hear about these cases where a game's source is libre licensed but not it's content and see what Stallman actually has to say about it.
Not for nothing, but there are many network/online games that have both source and content libre licensed. Here are a few:
