5 apps for teachers

I'm presenting this afternoon on technology use, and I thought I'd try and introduce a variety of tools to teachers (I'm aiming for 5 tools), and then let them brain storm ways the tools might be useful for them. Hopefully everyone will find at least one tool useful. The last time I presented on technology tools, I shared 30 tools in 30 minutes, which is enough time to see that a tool exists, but not enough time to see what it's uses are.

Here is my presentation from last year.

My challenge to you as a reader of this blog. Share with me any really useful applications that could be used by a wide variety of teachers that aren't already on this list. Bonus points if they are free. Oh, and it has to work on any platform.

Update: Here is my presentation for this year. Let me know if you can think of a better application for me to include than the ones I have, and the applications listed in the presentation above.