I converted all the Confluence instances ~1year ago to Xwiki[1] and some smaller one's to Fossil[2].

Both are great and opensource, i am really happy about the decision...thanks Atlassian!

[1]https://www.xwiki.org/xwiki/bin/view/Main/WebHome

[2]https://www2.fossil-scm.org/home/doc/trunk/www/index.wiki