Digital Garden

There's Hubzilla and it's wikis:

Hubzilla wikis are available out-of-the-box for any channel that enables them in their channel settings. You can create as many wikis as you like, with as many pages in each as you need. Hubzilla at its core is a decentralized publishing platform, so you can set permissions that allow only the people you want to have access to your wiki.

The magic of a Hubzilla wiki — the special sauce that sets it apart from the rest — is that you can give people read and/or write access even when they don’t have an account on your server. This is revolutionary web technology, folks. There is no central authority or single point of failure here. This is decentralized access control that works now. And it can work for you and your organizations today.

And:

Another great feature that integrates directly into channels is Hubzilla’s wiki system. Users can create an indefinite amount of wikis for a given channel, and create markdown-formatted pages for each wiki.

Creating wiki pages and formatting content is fairly straightforward, and provides the basic set of features for what you’d expect from a wiki system. Pages can link together, images can be embedded from your photo albums, and changes can have a revision message included for posterity.

It’s also possible to compare changes between revisions and revert to earlier versions of a page, which could be useful in situations where multiple people are editing the same wiki.