I've written about a couple of free systems recently which allow you to create business diagrams, charts, flowcharts and so on. Can you tell that I needed to create just such a thing and so have been researching the subject in depth?
Anyway, here's another one that's really good, free, and has lots of features. Create your masterpiece right in your browser, then save it to your PC or to your OneDrive, Google Drive or Dropbox account directly.
The system is called draw.io and you'll find it at http://www.draw.io