Storybird, a tool for writing digital stories is great fun and easy to use. Set up an account (free) – choose your art work and get writing! Students under 13 can sign up with parental permission. Emma wrote this story on revision. (Mark who ‘hearted’ her story is the creator of Storybird!)
For users of any age, Instablogg is a really easy way to publish a blog post. No registration is required, simply write and publish! You can easily share a link to your post.
Purdue University Online Writing Lab has extensive resources to help you improve your writing skills.
Harvard Generator is a free tool that allows you to quickly and easily format references and sources in the correct Harvard Referencing Format. The generator helps generate the correct format for a variety of sources.
Create a comic strip with Make Beliefs Comix, you can write in English, French, German, Spanish, Italian, Portuguese or Latin! This is avery simple site to use and requires no registration. Email the comic to yourself and create a link you can then share with anyone.
Another site where you can create a comic strip or a book is ToonDoo.
Posterous provides a very simple way to publish online content for students over 13. Simply send an email to Posterous with any attachments and they will publish the content and send the URL. There is an option to password protect the content. See Posterous FAQ for further information.
Penzu allows users age 13 and over to keep a journal online. The default setting is private, users can choose to make their content public if they choose; a link can be generated for an entry which can then be shared with others. The free version is intended just for writing, hyperlinks are not possible for example, though it is possible to upload images. Note that you can try it out before signing up.