Guile is an implementation of Scheme. As for why not CL, Stallman has expressed his dislike for CL, especially as a scripting language a lot of times over the y

Guile is an implementation of Scheme. As for why not CL, Stallman has expressed his dislike for CL, especially as a scripting language a lot of times over the years. Which is pretty funny because a lot of the criticisms he has about it (like the namespace system and keyword arguments) are in Guile now.