I am having way too much fun for a Monday morning playing with Kerpoof! There are a lot of fun things to do on this site, mostly relating to reading and writing, but could be applied in other ways. You can see a short introductory video about the site here, but I mostly just played with some of the elements to get started. There is a teacher link that allows you to set up free teacher accounts, but I have not tried it yet as I could access many pieces without it. There are some parts like the Make A Movie that wanted you to buy the scene at the Kerpoof store first, so I would suggest testing the teacher account before you have students rush into it. I imagine it would be best to have one if you use it with students though to allow them to save their work. You are agreeing to moderate your group if you do so however. You can see more about this and other elements here in the FAQ section.
The first ideas are to use Kerpoof for writing, spelling, genre writing, etc. but there are so many other places you can take it. The spell a picture is rather fun and a great way to make spelling fun, but also a great way to practice content vocabulary. Make a picture about a certain biome and only include things you would find there, or make a mystery scene or a science fiction scene all while practicing spelling and having fun. The Tell A Story or Make a Movie would be fun ways to teach genre through the student's storytelling, or have them use it to create a report about something they are learning. There are a ton of ideas on the lesson plans page as well.
There are lesson plans, pdf tutorials for each section, classroom ideas and more, but the best way to get started in my opinion is to just play!
How would you use Kerpoof in your classroom?