Scratch is a very easy to use and learn language designed by the MIT Media Lab mainly intended to introduce programming to children aged 7-16.
An Arduino extension is available on ScratchX, a Scratch sister site hosting experimental extensions. See the instructions for the experimental Arduino extension for Scratch.
The source code of the previous (desktop) version of Scratch has been modified by another team to produce S4A which reads Scratch programs but contains extensions to utilise a subset of an Arduino's input/output facilities.
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