Infuse Learning caught our attention as a new online system to try out. The reason we like it is because you have the ability to obtain drawings from participants. You can also push images to participants.
The teacher must use a computer to facilitate an Infuse Learning session, while participants can be on any device connected to the Internet. Using iPods and iPads allows for the easy to draw capability.
How engaging is it to have all students work through a math problem, then have them submit their work and share the responses. Possibly as a quick check have students label the parts of an image, say cell structure, and send in their results.
Infuse Learning also allows you to download and save responded entries from participants. Each drawing response is a separate page in a pdf file. Thinking outside the box, you could have a class of elementary students create a quick picture book by submitting their drawing, then the saved responses are collected in one pdf file.
There are many other features with this online tool, as these are a couple of ideas that seem well suited for iDevices. It's a resource well worth checking out.