Doceri is a free app much like ShowMe, Educreations or Screen Chomp that lets you create a video recording of drawings with narration. The feature that Doceri has that the others don't is that Doceri lets you save the recording directly to the camera roll. Once it's on the camera roll you can easily add it to Keynote or iMovie projects or email it. Plus there's no login required!
Check out this tutorial for recording and sharing a Doceri screencast.
(Click this link to view the video on the web if you're reading this blog post via email. http://www.safeshare.tv/w/UdnBIcLjGv)
Doceri also has a Pinterest board with several other tutorials and ideas for using it in the classroom.