Federated Wiki sites share pages circulating within a creative commons. A single-page browser application can read from many sites at once and save changes in that browser. Users who host their own sites can login there to have their edits shared back to the federation as they edit.
You can edit your copy of these pages by toggling the "wiki" link at the bottom of the screen. Press [+] to add more writing spaces. Read How to Wiki for more ideas. Follow Recent Changes here and nearby.
I've made notes under Matthew's Wiki Setup which may or may not help you get started. If you're new, it'd be better to read Host a Site first.
Ward hosts a search engine that lets you search across the Federation. Search 
This is a little better than search from a single Wiki as that only includes content in your Neighbourhood. About Neighbourhoods
We publish federated wiki software as a Node.js package ready to run on a variety of platforms. This is usefully run on a personal laptop or an industrial server in the cloud. Most people get started by joining a community and launching sites and/or servers with their help. The server software supports a multi-tenant "farm" option useful for small groups or heavy users. npm
A community of open-source developers maintain both the client-side and server-side applications most frequently used to browse and edit pages. Pages themselves are composed of paragraph-sized items of various kinds. This same community provides a core set of plugins for rich content pages and a variety of experimental plugins that push boundaries of web computing. github
Ward Cunningham started the federation in 2011 with a workshop project called Smallest Federated Wiki or simply SFW. The data visualization and sharing mechanisms were supported by Nike's Sustainable Business and Innovation group. Early history has been documented in a series of video screencasts. Search for "video".