As far as Confluence competitors go, in the vicinity of 2010 there was a lovely MediaWiki fork called DekiWiki (later MindTouch Core). It was easy to set up and use, fast, WYSIWYG editing, attachments. Unfortunately Mindtouch (the company) pivoted into- well, I never quite understood what, but it didn't involve developing deki and it became defunct. It would have been very interesting to see where it stacked up today if it was kept alive.