Lots of people (Red Hat, Richard Stallman...) charge money for open-source software, so this seems a moot question.

This case is a bit different though: Chessbase (unlike RH and RMS) didn't tell anyone their product was open source, but pretended it was their own proprietary work and that it was better than the leading open source engine that it was stolen from.

I don't think so. Red Hat Linux - the software - is free under GPL. Red Hat the company charges for support, training, and documentation. ChessBase charges for the software, which means they're either not compliant with the terms of GPL, or there's some other aspect of the software they're not obligated to share. I'm particularly interested if it's the latter.

But I'm just wading into this subject matter, so others chime in if I'm missing something :)

> ChessBase charges for the software, which means they're either not compliant with the terms of GPL, or there's some other aspect of the software they're not obligated to share.

It's very clear from the story that it's the first one: they're not compliant with the GPL. At least that's what the Stockfish authors are claiming. They're pretty obviously acting in good faith and appear to be correct in their claim. ChessBase haven't laid out their side of the story other than their marketing materials saying "we developed the software in house and it's better than that open source stuff" and I wouldn't expect them to have a defence based on anything other than technicalities. You won't be seeing a blog post from them, because their lawyers have told them to say nothing.

It’s very clear that Stockfish _claims_ ChessBase violated the terms of the license (and by corollary, ChessBase claims they didn’t) but it’s not at all clear who’s right until the litigation process plays out. One thing I will say is the perceived superiority of ChessBase’s fork (“better than the open source stuff” as you say) has no bearing on either claim.

As far as I know, Red Hat does not provide compiled binaries without a (typically paid) Red Hat license.

The point is, Red Hat is not a comparison because users can build, understand, and redistribute their version of Linux for free (in accordance with GPLv2). Not so with ChessBase.

The point being made is that the "for free" part of that sentence doesn't actually exist in the GPL. You can modify GPL code, then charge for access if you want (which, IIUC, Red Hat does). You just have to give it to whoever you sell it to under the terms of the GPL, which means your customers could give it away for free if they so choose.

    > which means your customers could give it away for free if they so choose 

If you’re only guaranteed one sale before your first customer undercuts you, then it is free “in the limit”. That is why Red Hat sells everything ancillary to the software itself (quality assurance, training, documentation, support, etc.)

ChessBase is selling the software, and they aren’t getting undercut because they are not redistributing everything the customer needs to rebuild it from source. It will be interesting to find out what that is (neural net weights, or whatever) and whether the court upholds that this is not copylefted under the GPL.