Imagine I've written a game and I want to make it free software. Am I also required to make the game server software free software because the game uses it to connect to other players to play against?
Imagine I've written a stock ticker and I wish to make it free software. Can I charge for the subscription to the stock information, even though the software serves little purpose without paying for such a subscription?
I'm also interested in revenue sources for free software that go beyond charging for distribution or support, that counteract one person purchasing your software and then distributing it themselves and undercutting your prices.