Thanks for suggesting BookStack [1]. I did initially create the project as a free open-source alternative to confluence as I didn't want financial approval being a limiter to documentation collaboration.
One of the main things to consider with BookStack is the semi-fixed Shelf > Book > Chapter > Page structure (Where pages have content, chapters & shelves are optional, and Books can be within multiple shelves). For some this structure is limiting, For others it helps drive organization.
