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It is possible to sell Scratch projects. The creator can then attach any license they wish to the code. Just remember that once a project is shared in Scratch, anyone can download, remix, reuse, and sell it as told in the terms of the CC-BY-SA 2.0 license. This means that you might want to un-share your project from Scratch if you are or plan on selling your project, but the Creative Commons License can never be canceled. It is probably the most practical to sell either a CD with the project or a compiled EXE/APP. Selling copies of the Scratch program itself is not allowed, but according to GPLv2, the program generated by the source code can be sold with its source code.