A Scratch SB file is a program created with MIT's Scratch application. It contains source code written in the Scratch programming language and can be compiled into a .JAR file.
About MIT Scratch
Scratch is an application development program created at MIT (the Massachusetts Institute of Technology). It is designed to enable students from ages 8 and up to develop basic software programs while learning important mathematical and computational concepts at the same time. Completed Scratch programs are saved as Java archives, which can be played on any platform that supports Java.