Everything you write is private, as it should be, but you can share stats it generates – things like WPM, time spent writing, commonly used words, and emotions it infers from your writing.
The site itself is beautifully minimalist. You’re given a big, blank page to write in, with a subtle word count. Once you’ve hit 750 words, it waits until you’ve stopped typing, then pop up a notification. You get the feeling that a lot of thought has been put into the design.