Read, Write, Think produces, so it was no surprise that I also loved the app Venn Diagram. It has a very user friendly interface for students so it doesn't take them long to be up and running. Students can create a 2 or 3 circle venn diagram and add items to each circle. Each item can also have a description so if students want to print out their creations, they will have two pages - one page with the diagram and items and another page with the items and descriptions.
Students can save their work if they don't finish in the allotted time because they have to create an account to get started. Don't worry, their account consists of their name only so you don't have to be concerned about complicated account creation. Students will have to go back to the same iPad to find their account because it is tied to the iPad. When students complete their work, they can save it to the camera roll or email it to the teacher.
Read, Write, Think also has a web version of the Venn Diagram program so if you don't have enough iPads for all of your kiddos, don't worry. They can grab a computer or Chromebook and get started.