Check these out!
There are many websites that offer free software for presentations. In some cases you will create and account in order to use the software and in others, you can just begin creating what you need! Check these out:
Gliffy is diagram software for venn diagrams, flow charts, org charts and many more! If you use the free software, your charts will become public. If you pay for the next level of software, your charts will remain private.
desmos.com Online graphing calculator