Have you tried using Google Docs in your classroom yet? Students are able to share their document with you and the other students in their group. Group members can write within the document simultaneously. Writing can continue outside of the classroom and students can chat with each other via the chat pane as they write.
Ask your students to bring their laptops, or assign groups and then make sure at least a couple of students in each group bring his/her laptop to class.
This video shows how one instructor is using this in her classroom: