Free wifi, for how long?

How can something this good be free forever?

It’s not free forever. It’s free for the intended audience. It’s a basic broadcasting model; the listener gets the message for free because someone else is paying for it. In this case, the best model to compare it to would be religious radio broadcasting. It gets paid for by people who believe in the message, and are willing to donate to the cause. Alternatively, some advertising might be involved for areas that are not competely oppressed.