Flowdock was a more opinionated service and that was IMO to it's detriment. It's primary usage wasn't internal communication but rather communication around social media.
Slack took the simplicity of IRC and gave it a modern interface with things like showing a preview when you link. easily share files etc.
> It's primary usage wasn't internal communication but rather communication around social media.
What makes you think that? I don't see any connection between Flowdock and social media. As far as I can see, it's purely an internal communication tool with easy file sharing, hooks for external services as GitHub, and so on.
As far as I remember it started as that. But maybe that's not accurate. I just remember them pushing how twitter could be monitored and then important tweets could be send around the organization to deal with them.
That feature is a flow (or channel) specific "inbox". You can add different sources such as e-mail, GitHub pushes, CI results, or the Twitter you mentioned. Basically looks like an in-channel RSS feed of different sources. Personally I love the feature.
A neat thing is that you can start a discussion thread from any of these items, so the context of the discussion is clear.
Oh I like FlowDock a lot was just trying to explain how I believe Slack won over it by being less opinionated about how it approaches conversation. It's IRC core functionality and then apps on top for specific needs.
Flowdock went a little further ahead when it came to how they constructed the base communication.
Slack took the simplicity of IRC and gave it a modern interface with things like showing a preview when you link. easily share files etc.