There's things built for entirely different reasons that can be used as a federated Wiki if you wish, like Fossil (a federated version control system with a Wiki)

https://www2.fossil-scm.org/home/doc/trunk/www/index.wiki

Note that Wiki federation has a whole bunch of potential issues if you try to allow automatic updates from arbitrary users. Wiki servers rely heavily on antispam measures which often require a lot of analysis of the user's connection, data which often isn't available over federation, so submissions by others have to be validated manually. Fossil being a version control system means it is more of a mirroring friendly Wiki than truly federated, but you can set it up so that mutually trusting mirrors can replicate each other's validated commits/updates.