Amy Editor includes support for real-time collaboration on a document over internet. You simply invite a person to collaborate on a document you opened and after receiving an invitation code, the person opens the same document with current state. You'll immediatelly see his/her changes as she sees yours. There is no limit on number of collaborators on one document, as well as there's no limit on number of opened collaboration sessions. It's pretty much possible to work on multiple documents with other people, acting sometimes as invitor, sometimes as invitee.