Though these tools you can draw, edit, save and share your diagrams like flowchart, network diagram, wireframe, Organizational charts etc. Most of them have free basic option or free trail that you could use and experience these tools.
I love this site. Every maths and business studies teacher should be using it. Children can buy and manage virtual shares at the London stock Exchange and the site is linked to real prices.
http://ictmagic.wikispaces.com/Maths