Just came across this video about draw.io. As we have a Confluence license from you guys, I was wondering if you got some more experience with this particular plug-in?
Please check out this blog article exactly on the subject and watch the video there. You will find all kind of info about this add-on and a comparison to Gliffy.
You can also download a free trial on the Atlassian Marketplace: https://marketplace.atlassian.com/plugins/com.mxgraph.confluence.plugins.diagramly/cloud/overview