The thing about Wikipedia is that users have the right to fork it, per its license, and have historically used it (see Encyclopedia-Libre). It's at least potentially a federated system, in a way that other comparable sites are not. Interestingly, the same is true of Stack Exchange/Stack Overflow: its content is openly licensed, so in principle you could use it to seed your own Q&A site if you objected to how the original was being run.