Google Drive
Google Drive is a cloud-based system for creating and sharing documents, and is a great way to be environmentally-friendly by reducing paper with the benefit of not having important documents “lost” on your desk or in your filing system. If you can use Microsoft Office, you can create Drive documents! The formatting and styles are parallel to MS Word, Excel, and PowerPoint. You can also create forms and drawings.
You can create documents directly in Drive
You can upload MS Office files onto Drive (occasional formatting issues may result that will need to be adjusted when saved as a Google Doc)
You can share documents, etc. with individuals and groups - How to Share
When sharing, you can specify “read only,” “can comment,” or “can edit” by individual for each shared document, allowing for different levels of collaboration
Related Link - iOS app for Drive in the App Store