An open source turtle that understands a programming language
An amazing suite of tools right out of the box: an integrated interpreter, documentation view, code editor and graphical runner; built-in console;
Works on Windows or Linux. Windows has an installer program (packed with all dependencies), while Linux will use directly the .jar. It may work on Mac too.
Great A'Tuin is the Giant Star Turtle (of the fictional species: Chelys galactica) who travels through the Discworld universe's space, carrying four giant elephants (named Berilia, Tubul, Great T'Phon, and Jerakeen) who in turn carry the Discworld. The narration has described A'Tuin as "the only turtle ever to feature on the Hertzsprung-Russell diagram.
It is a student project (2nd year Informatic Licence, at Paris Diderot University); subject (fr): subject.pdf.