Snap! Build Your Own Blocks

Snap! is a visual, drag-and-drop programming language and an extended reimplementation of Scratch that lets users build their own blocks. It runs in the browser and is implemented in JavaScript, addressing the need for a tool that supports both introductory programming and more advanced computer science concepts.

The language features first class lists, first class procedures, and first class continuations, along with first class sprites, costumes, and sounds. These capabilities allow users to create custom control structures, implement data structures such as trees and dictionaries, and use higher-order functions. Snap! is presented by the University of California at Berkeley and runs directly in the browser.