Q: Why is it called Snow?
A: Snow originally stood for "Scheme Now," and is in part a reference to the analogy that Lisp is a ball of mud. Add anything to Lisp and you still have a ball of mud - it still looks like Lisp. The same can be said of Scheme, except it's cleaner. You can also use the backronym "Scheme Networked Object World."
Q: How I can use or install these libraries?
A: Any R7RS compliant implementation should be able to use these libraries. Chibi-scheme as of version 0.7.3 comes with a command snow-chibi which can automatically search and install R7RS libraries for itself and other implementations.