draw.io for Confluence Cloud is a plugin for Atlassian's Confluence Cloud product.
draw.io provides embedded diagramming functionality to add a range of diagram types to Confluence pages. All diagram data is stored only in Atlassian's cloud, directly from your browser (it doesn't pass through our servers during save/load).
IMPORTANT - 22nd Feb 2017. We've had around 5-6 reports of draw.io completely failing to operate very suddenly. In all cases it turns out that all add-ons used on those instances fail, the bug is Atlassian's. It seems they have deployed a version of Confluence Cloud to a very limited number of users where add-ons simply do not function. We strongly encourage you to file a support ticket with Atlassian, https://support.atlassian.com/servicedesk/customer/portal/23 , to mark it as top priority and indicate that you view the issue as critical (assuming you do). Atlassian have indirectly confirmed this is the case on this thread.