Tux Paint for the Sugar environment
and the One Laptop per Child (OLPC) "XO-1"
Newer versions of Tux Paint have been released; you can download the source-code.
Tux Paint for Sugar comes as a single bundle that includes both the main program and the add-on 'stamps' collection.
(For more information on the "Sugar-ization" development of Tux Paint, see the Tux Paint page at the OLPC Wiki.)
Tux Paint & Tux Paint Stamps.
Tux Paint 0.9.20 & Stamps for Sugar
Tux Paint 0.9.20 for Sugar Source
A small Python script has been created that you can use on the XO-1 to take the most recent webcam photos from the Journal and insert them into Tux Paint, so you can paint on them.