He gives a good overview of what it offers, so I’d encourage you to go directly to his post.
I’d like to highlight one area of the site that I’m adding to The Best Websites For K-12 Writing Instruction/Reinforcement. It’s called Your Story Box, and is basically a simple cloze (gap-fill) activity where users fill-in the blanks with images that are converted into words. Audio support is also provided to the text.
It’s a great exercise for Beginning English Language Learners.
I’m also adding the link to that activity to my website under Writing.