Scratch is much simpler and less powerful than Lisp, missing many of Lisp's most important features, like first class functions, complex data structures, and other first class objects. You can't even pass lists around as parameters, or include lists in other lists, and it's missing homoiconicity (representing code as data), reflection, macros, special forms, or even user defined blocks and control structures, etc.
But Snap! goes way beyond Scratch, since it was inspired by and visually similar to Scratch, but is just as powerful as Scheme, including functions and everything else as first class objects, lexical closures, continuations, user defined blocks, macros, special forms, etc. It's much more powerful than Scratch, but uses the same visual interlocking block syntax.
