I created a web clip of the website chalk.37signals.com. It is a simple blackboard with 2 colors of chalk and an eraser. My students use it for all sorts of activities, basically like using an individual whiteboard, but without the smell of 23 markers open at once. By using the screenshot option, they can save and email me their work.
As we transition to common core standards in my district, we have been discussing the importance of "number talks"--having students think of all the ways to equal a given number. I haven't done anything this until today. Today I gave them the number 16 and asked each of them to show 1 way to equal that number on their chalk screen. As a class we came up with the option of addition, subtraction, multiplication, division, place value, skip counting, and drawing.