Scratch is a simplified version of Lisp/Scheme, without many important features like first class functions, lexical closures, continuations, special forms, the ability to define your own blocks and control structures, and everything being a first class object that you can bind to variables, pass around, and return from functions.

Snap! supports all those important features of Scheme (its original name was BYOB for "Build Your Own Blocks"), with the visual interface and sprite and stage and turtle graphics of Scratch, plus it's written in JavaScript, so it's efficient and easy to integrate with existing JavaScript libraries (see "etoys2learn"!), instead of running in a monolithic Smalltalk virtual machine.