#FreeSoftwareAdvent
A piece of free software I rely on at work is #Dokuwiki: https://www.dokuwiki.org
We run it on a simple Apache & PHP VM. No need for a database, connects to LDAP for user accounts (optional).

It's old-school but it also has a wysiwyg (what you see is what you get) plugin for editing pages - which doesn't support all formatting features (pending more funding from interested users). But it's there so the non-techy people can clicky-click their headlines and tables.