Now this is an online tool with a wealth of uses for teaching maths and using in general rather than excel / windows calculator.
Instacalc is an online calculator / spreadsheet mashup. It supports sharing, and blog embedding, and intelligently interprets what you type in. Check out the blog for a walk though of the features.
Here’s an example I just knocked up in two minutes, a little Pythagoras….
I think there is a wealth of potential here for use in the classroom, for homework and for blogging.