More than 23 million users sharing almost 28 million projects gives some small idea of the popularity of Scratch, which describes itself as "a programming language and an online community where children can program and share interactive media such as stories, games, and animation with people from all over the world."
A project of the Lifelong Kindergarten group at the MIT Media Lab, Scratch was recently celebrated in Ed., the Magazine of the Harvard Graduate School of Education, on the occasion of Scratch's 10th anniversary. When children were asked to share what they would tell a friend about Scratch, the top 10 responses included such terms as "excitement", "imagination", and "possibilities".
The developers of Scratch aim to help children -- generally from ages 8 to 16, although there is a version for younger children, ages 5-7, available as a free app called ScratchJr. -- "think creatively, work collaboratively, and reason systematically." There is no charge to use Scratch.
In addition to information for parents about Scratch, to enable them to understand how it works and to explain the guidelines of the Scratch community, the folks at the Harvard Graduate School of Education have created an online community for educators, ScratchEd, to enable them to share resources and stories. Scratch is a resource worth checking out.