"Free online diagramming application"... Create flowcharts that look professional and colorful. I haven't explored the site all the way to create anything yet, but wanted to capture the concept before I lost it.
Another educational use for twitter. Create a poll, tweet your question, gather your data, explore the data. Could be a social studies tool, a psychology tool, an English tool, a math tool, or science tool. I guess if you analyze the data you receive all the questions would be a math tool.