Scheme Implementations

So. I've been trying to learn Scheme, but the lack of a reference implementation has gotten me confused. I have installed scm, but I am still unsure. Therefore, so I must ask: What are the best Scheme implementations for a beginner? And what is this stalin thing I've been hearing about?

>>7
Hm. Since as a beginner I don't want to incorporate any nonstandard extensions as bad habits, I guess I will avoid it. Thanks for the information, though.