According to Wikipedia, it's still in existence, but has evolved to specialize in creating education and training apps, so may not be quite the same as I remember it anymore.
EDIT: The link to Runtime Revolution was added while I was writing my comment. It's an upgraded version of HyperCard for networks. I was thinking more along the line of a least common denominator replacement for HyperCard.
It looks to be exactly what you're after.
An accomplished HyperCard user was justified in feeling like the "master of all he surveyed." Even trying to cultivate such a feeling in the users of "modern" computing systems is akin to building an amusement park on quicksand.
That said, TileStack is what made me realize I don't want HC as it was; I want HC as it was, plus networking functionality. It just doesn't feel anymore like there's much point to writing apps that can't connect people to one another.