Google Docs is a free educational tool that can be used for collaborative writing and presentations for students. The web based software is a great resource for teacher looks to promote writing on the web. Students can work together on separate screens at any time. A final project can be a report, book review or presentation worked on by every student. The service even allows teacher to see changes and writing made be each student at specific times by comparing new and old revisions.
I have posted a video of various teacher and administrators who find Google Docs to be a valuable resource: