Google Docs is an application from Google that allows registered users to work on and store their documents online. You can create documents from scratch or upload documents in different formats (Word, OpenOffice, RTF, HTML, or text files) and work on them online. Your documents are available to you from any computer with an internet connection.
You can invite others to view or edit your documents, which means that it is useful for collaborative work or where you want feedback from others.
You can view the revision history of your documents and retrieve earlier versions. You can download your documents to your computer, send them as email attachments, publish them as webpages, and post them in your blog.
Google Docs is a free service but you have to register to get an account (if you use Gmail, you already have one).