draw.io is a completely free diagramming Docs Add-on, no registration is required.

draw.io focuses on providing enterprise grade: 

- Scalability 
- Reliability 
- Security 
- Availability 
- Privacy 

The key advantages of draw.io for a company basing their cloud storage strategy on Google Drive are: 

- All application data is stored only in Google Drive. 
- Diagram model is only transmitted directly between browser and Google Drive, server-side data is subject to Google security only. 
- draw.io only operates from the https domain, using industry standard SSL encryption. 
- Multiple Google accounts are supported, including any number of Google Apps for Business accounts. 
- draw.io is hosted on Google App Engine and statically serves a fully operational JavaScript application. The scalability and reliability of draw.io correlate with that of the serving infrastructure only. 
- Your existing backup of Google Drive files will include all draw.io files.