It's funny, we were early (?) adopters of Flowdock, back in about 2012, on one particular project. We used it fairly happily for a year or so, and then just sort of forgot all about it and drifted back to Skype (I think with a brief flirtation with Hipchat whilst we were doing something Atlassian-centric), probably because Skype was free and Flowdock wasn't. In around 2014 suddenly everybody started using Slack, and I found myself wondering how, really, it was much of an improvement over Flowdock and why it gained massive traction. (I suspect marketing and the fact that Slack is effectively free for many types of teams.)