The lone admin and developer of kbin there had some personal concerns. He meant well, but I think the whole thing was a bit more than he ever intended to take on, especially after the reddit API influx of users.

kbin got forked to mbin, which is still being developed. fedia.io runs on it, others too, but I couldn't say which. As far as "apps" go, I have no problem just using the mobile site for it. mbin/kbin have some limited support for microblogging ("Mastodon" - but don't get me started on terminology), where lemmy does not.