The Racket website at racket-land.org is served by Racket [and mostly written in it, too]. HN is [or at least was] written In Arc and Arc is/was written on top of Racket [or one of its predecessors].

If Racket is winning it may be because its ties to acadamia provide a stable working group who can work on it as part of their day job and a constant stream of grad students who implement their work in it.