Scratch is a programming language that can create interactive stories, games and animations easily.
Official Web site: http://scratch.mit.edu
Online version (Scratch 2.0): http://scratch.mit.edu Click "Create new, 新建"
Installation version (Scratch 1.4): http://scratch.mit.edu/scratch_1.4/
Resources:
Scratch 1.4 reference guide: http://info.scratch.mit.edu/support/reference_guide_1.4
or http://download.scratch.mit.edu/ScratchReferenceGuide14.pdf