What's in a Tool?

Tonight's the first night of a ten week course I'm teaching on social tech and education at Johns Hopkins.

Here's a question directed to the folks out there using social tech in the classroom on a regular if not daily basis: if you were teaching the course, what are a few Web tools you'd insist that every new teacher learn about in grad school?

And the classic part two: Why? What is it about these tools that makes understanding them so essential to teaching in the digital age?

Comment away, I'm looking forward to reading your ideas, sharing them, and debating them with my students.