"Paul Graham’s programming language Arc, a dialect of Lisp, was built on top of Racket." Since that statement occurs in a section about Racket languages, I should probably clarify. Arc isn't technically a Racket language—that is, it doesn't use any of Racket's facilities for defining new languages. It compiles to Racket (and so you're all using it right now), but has its own distinct implementation. Historically, Arc…
I think it compiled to MzScheme first.
http://www.reddit.com/r/programming/comments/bstl/arc_lisp_d...
A friend told me he used to track developments in Arc by noticing when pg had switched mailing lists. :)