Hi,
is the Diagram Application:
Diagram Application (XWiki.org)
Still available. I am using Version 15.1, the search in extension points me always to Diagram Application Pro. Now the licence is exired and it is not usable anymore.
regards
The free version is still available but I don’t think anybody has worked on it recently, see https://extensions.xwiki.org/xwiki/bin/view/Extension/Diagram%20Application
The search will show it, make sure you select also not recommended extensions.