There are implementations which implement the standard, slight variations of it (lower case identifiers, ...) or large extended versions of it (+ MOP + CLOS everywhere + ...).

There are also derived languages like Stella, L, SubL and others which implement some kind of subset.

Then there is ISLisp, which is very similar, but slightly simplified.

Thanks. I changed the wording to reflect this. Is it better now?

Yup, thanks!