Creating mathematical diagrams for free

To excellent options for creating mathematical diagrams are Google Drawings, and Diagram.ly. The chief advantages of Google Drawings is that you can save, edit, and collaborate (good for group projects) on your drawings later. The biggest advantage of Diagram.ly is that it doesn’t require sign-in (useful for working with students), and it has many more options for creating your diagrams.

Cylinder with 20cm diameter

Created with http://diagram.ly

Created with Google Drawings