On Morning Pages, you can write a stream of thought journal entry, but with a twist. The letters you type slowly fade until they are almost completely transparent. If you look closely, you can see what you wrote, but this feature keeps you from editing or getting hung-up on your words so that you can more easily enter a flow state.
You can click the magnifying glass in the top right corner to reveal your text when you're done. Click the scissors to copy it. Having your writing disappear (temporarily) may make it easier to try a stream of thought writing exercise.
I keep a journal in my iphone notes app, but this seems like a fun place to do the actual writing before I copy and paste it into my notes. Losing track of how much I've written also helps me focus on my present thoughts. I like how simple this site is to use!
See also: Midori Traveler's Notebook, an invaluable tool from Japan