I don't know why Slack is seen as a first mover; Hipchat, Flowdock, etc all existed beforehand. Slack seems to have raced ahead by ramping up marketing and not just focussing on B2B sales.
In terms of tech I actually see Slack as behind in the default product (no threaded conversations >_<), but maybe the ecosystem they're trying to foster will actually be useful or maybe the money they've spent on marketing will be irrelevant and they will collapse due to overfunding.
In terms of tech I actually see Slack as behind in the default product (no threaded conversations >_<), but maybe the ecosystem they're trying to foster will actually be useful or maybe the money they've spent on marketing will be irrelevant and they will collapse due to overfunding.