Screen Chomp is a free app put out by Tech Smith. They also are the makers of Ask3, which I blogged about recently. Screen Chomp is a nice way for teachers to create quick and painless tutorials/instructional videos. (Don't worry, it only records your voice and markings on the screen. No faces!) Once the teacher makes the video, they can send the link off to their students through email, Edmodo, or their blog for viewing. Some students like the idea of being able to watch the video (or specific parts of the video) to ensure understanding of a topic.
Students can also use Screen Chomp. They can use it to import pictures to share knowledge, demonstrate understanding, or even make a full fledged presentation for the entire class to view.
Check it out for yourself. Practice first with a few mathematics problems. Learn to import pictures so you can draw diagrams and make captions. I'm sure you can think of many ways Screen Chomp can assist you in your classroom.
Update on 5/20/2014:
Students under the age of 13 cannot export their work. Some teachers have found resourceful ways around it. For example, have students do a "gallery" where everyone can travel around the room to view.