Have there been commercially successful free software games?

If the code was Free Software, how would you sell in-game purchases? Note that if it were just 3d models for your character, others could sell them too, likely cheaper without the overheads of developing the base game. Note that the article is advocating for multiplayer code to be open too.

I love free software, but I don't see how it was works in practice with games unless you're talking about open sourcing years later. Games seem different in usage and development than operating systems.