What you have to remember is save the address in your bookmarks or you will never be able to see it again (unless you have a brilliant visual memory).
QuietWrite is described as a peaceful place to write. Just click and write.
Entri is useful for writing rough drafts of articles, jotting down ideas and sharing them with a specific group of people. Direct access to Twitter. No signup required.
Stashsite is advertised as a site for making a downloadable page for an e-book or presenting schoolwork to the teacher in a nice fashion.
Update: Stashsite is gone!
Jottit works in a similar way - you can write or post a text and edit it. The site also lets you format the page - you can change the background colour and fonts.
ShortText is an extremely simple tool, it lets you type or paste any text. There is also a possibility of adding a link to a video or an image. You can allow comments on the page.
DinkyPage looks a little more complicated but it serves the same purpose as the sites mentioned above. There are more formatting options than with other sites and you can get a fairly nice web page with images and links if you spend some time on it.
There are a lot more sites which offer online writing possibility but either they are more complicated or require sign up, that's why I have not mentioned them in this post.