I have created a new OLPC XOactivity called the RetroScope. It shows you live video, but with a zero to 10 second delay. It is super simple, but can be a lot of fun!
This activity builds on the experimentation I did a year ago with the XO's camera, and is inspired by Nat's original idea for the RetroScope.
The source is 109 lines of python, and is released under the MIT license: