Storybird is a great tool that allows students to become authors. The user friendly format makes it easy for all age levels. Students love to see their writing become more than just words on a page.
This is a great resource. I just started to poke around at it but I can see where it would be beneficial for students to you across curricular classes.
I also think that Story Bird is a resource that students would find engaging while allowing them to improve their writing skills. I think that my K-2 students would enjoy this.