This is one of those applications that is always being rewritten somewhere. JWZ's law may even be relevant here: "Every program expands until it reads mail". It seems there is always a large group people out there working on messengers.
The question really is what made Slack special. Why is it the Slack revolution and not the HipChat revolution? What about the veneer has allowed it to become a pervasive trend, expanding into non-tech companies and being hailed as a permanent replacement for most emails? This is the only interesting question around Slack, since, as numerous other commenters have pointed out, it doesn't really bring anything to the table that the messaging space hasn't seen a good number of times before.
The question really is what made Slack special. Why is it the Slack revolution and not the HipChat revolution? What about the veneer has allowed it to become a pervasive trend, expanding into non-tech companies and being hailed as a permanent replacement for most emails? This is the only interesting question around Slack, since, as numerous other commenters have pointed out, it doesn't really bring anything to the table that the messaging space hasn't seen a good number of times before.