Recently I was introduced to Stixy (http://www.stixy.com/), and online collaboration tool. You need to sign up for a free account but your users, your students do not. If your district worries about privacy, you can password protect your Stixyboard.
When setting up a board you can add a note, a photo, a document, or To-Do as a prompt. Students will use the link you provide them to respond. Students can respond with a note, photo, document, or To-Do just as you set your prompts. Each student can respond to you and/or other students. Responses are posted in real time so a simple refresh of the browser shows you and your users what is currently being posted to your board.
Stixy is a website so nothing has to be downloaded. It can be accessed in school, as a center, or assigned as a homework assignment.
My example is set-up to have the students respond to a fractured fairy tale.