ShowDocument is an instant live online cross-platform collaboration tool used to quickly share documents with friends and coworkers. It allows simultaneous viewing of almost any common document type, including MS Office and OpenDocument formats, pdf, rtf, jpg, gif, png, txt, xml, and more.
The presenter uploads one or more documents and invites up to 50 colleagues to view it with him live. All the participants in the session see each others' annotations, markings, highlights, etc. There is a chat window to allow real-time communication among the participants and a whiteboard function.
Each participant can save the annotated document to his own computer as a PDF. The duration of a session is limited to one hour. ShowDocument is free.